Enfin : la première action au sens de l’art. 8 du Protocole No. 2 après Lisbonne et l’avenir du contrôle de subsidiarité

Assemblée nationale v Parliament and Council: a constitutional Case disguised as a migration Dispute

Advocate General Ćapeta’s Opinion of 4 June 2026 in Case C-553/24¹ is the first action ever brought under Art. 8 of Protocol No 2 on the application of the principles of subsidiarity and proportionality² since that provision entered into force with the Treaty of Lisbon. A minority of deputies of the French National Assembly challenges the validity of Regulation (EU) 2024/1351 on asylum and migration management³, alleging a violation of the subsidiarity principle.

The enduring significance of the proceedings lies in the seventeen-year lacuna that they terminate. Since Lisbon, Art. 8 has been formally available, constitutionally non-trivial in its implications, and entirely hypothetical in practice. Scholarly literature has accordingly addressed the Art. 8 remedy in predominantly prospective terms, treating the questions it raises as academic in the absence of any judicial determination⁴. Case C-553/24 changes that condition. It requires the Court to answer a question that the Lisbon settlement deliberately left unresolved: what kind of remedy is the parliamentary subsidiarity action intended to be?

The Opinion of Advocate General Ćapeta provides the first authoritative reconstruction of the constitutional identity of the Art. 8 action. That reconstruction is significant in itself. Yet its implications reach further than the Advocate General explicitly acknowledges.

Art. 8 of Protocol No 2: a Remedy unto Itself

The most consequential feature of AG Ćapeta’s Opinion is not what it says about subsidiarity, but what it says about the judicial architecture through which subsidiarity is enforced. Before addressing the substance of the action, the Opinion confronts a jurisdictional question: whether proceedings brought pursuant to Art. 8 of Protocol No 2 fall within the jurisdiction of the General Court under Art. 256 TFEU or belong directly to the Court of Justice pursuant to Art. 51 of the Statute, as for those touching upon the constitutional foundations of the Union legal order. As often happens in Union constitutional law, a procedural question quickly reveals itself to be a constitutional one. The answer depends upon the nature of the remedy itself.

Is Art. 8 merely a specialised variant of the action for annulment established by Art. 263 TFEU, distinguished only by the identity of the applicants and by the limitation of the grounds of review? Or does it constitute a distinct constitutional mechanism designed to protect a particular dimension of the equilibrium established by Art. 5 TEU? Advocate General Ćapeta adopts decisively the latter position, departing from much of the pre-litigation literature that had treated Art. 8 as little more than a lex specialis of Art. 263⁵.

A lex specialis relationship presupposes modification at the margin of a general norm that otherwise remains applicable. The Art. 8 action, however, differs from ordinary annulment proceedings not in peripheral respects but in three constitutive ones. First, the standing of national parliaments and parliamentary chambers derives exclusively from Protocol No 2 and is entirely external to the taxonomy established by Art. 263 TFEU⁶. Second, the permissible grounds of challenge are radically narrower, confined as a matter of constitutional structure to the single allegation of a subsidiarity violation (whether authority has been exercised at the appropriate level of governance). Third, the function of the remedy is specific: Art. 8 is neither an instrument for protecting institutional prerogatives nor a mechanism designed to compensate for the restrictive standing requirements governing direct actions. Its purpose is to preserve the constitutional logic of Art. 5 TEU. The remedy forms part of a broader architecture through which the Treaties seek to reconcile effective Union action with the continued relevance of national and sub-national decision-making structures. Its procedural features – governing time limits and the effects of annulment – may be borrowed from Art. 263. Its constitutional rationale is not⁷. A remedy possessing a distinct constitutional rationale requires a distinct understanding of its object and function.

It is precisely at this point that the broader implications of the Opinion begin to emerge. If Art. 8 is not merely a specialised annulment action, the question immediately arises as to what kind of review is appropriate to its constitutional identity. The answer proposed by AG Ćapeta is strikingly restrictive. Yet it is precisely that restriction which gives the Opinion its lasting constitutional significance.

A ‘single Question’: the constitutional Perimeter of Art. 8 of Protocol No 2

Having established the autonomy of the remedy, AG Ćapeta proceeds to define its object with unusual precision. The result is not an expansion but a contraction of subsidiarity litigation. Throughout the Opinion, subsidiarity is carefully insulated from neighbouring constitutional principles whose practical interaction has long generated uncertainty in academic writing and judicial practice. What emerges is a conception of judicial review characterised less by restraint than by containment: a deliberate effort to confine review to the precise constitutional question entrusted to the Court by the Treaties.

The starting point is Art. 5 TEU itself. Although frequently invoked as if it articulated a single doctrine governing the exercise of Union authority, Art. 5 establishes three distinct constitutional principles operating at different analytical stages. Conferral determines whether the Union possesses the competence to act. Subsidiarity governs whether that competence ought to be exercised at Union level. Proportionality regulates the intensity and content of the measures adopted once the decision to act has been taken. The architecture presupposes differentiation rather than overlap. AG Ćapeta takes that differentiation seriously. Several arguments advanced by the applicants sought, in substance, to challenge the existence or scope of Union powers in the field of migration management. The Opinion refuses to examine such claims through the lens of subsidiarity. Arguments concerning the limits of Union competence belong to the principle of conferral; they do not become subsidiarity arguments simply because they are raised in proceedings brought under Art. 8⁸. The distinction is constitutionally significant: it prevents the parliamentary subsidiarity action from evolving into an alternative route through which national parliamentary actors may contest the legal basis of Union legislation⁹. The same logic governs the relationship between subsidiarity and proportionality. The temptation to conflate the two principles is understandable – decisions on migration, environmental protection or digital governance inevitably raise questions both about the level at which authority should be exercised and about the intensity of intervention considered appropriate. Yet the Opinion consistently resists any tendency to collapse one inquiry into the other. Objections directed against the content of legislative choices, the burdens imposed by regulatory measures, or the substantive balance struck by the legislature are characterised as proportionality concerns rather than subsidiarity concerns¹⁰. For AG Ćapeta, subsidiarity concerns neither the intensity of intervention nor the desirability of legislative choices; it concerns only the prior question of whether action should occur at Union level at all. An analogous conclusion emerges in relation to national identity. Arguments grounded in constitutional identity, essential state functions or institutional autonomy are not absorbed into subsidiarity review. Whatever their importance, they derive from Art. 4(2) TEU and remain governed by the doctrinal framework developed under that provision.

The cumulative effect of these exclusions is a remarkable operation of judicial containment¹¹. The Court is assigned one question, and one question only: whether the objectives pursued by the contested measure could have been sufficiently achieved by the Member States acting individually, and whether, by reason of their scale or effects, those objectives could be better achieved at Union level. But the success of that operation generates a new difficulty. The more rigorously subsidiarity is separated from conferral, proportionality and political disagreement, the more pressing becomes the need to identify what meaningful subsidiarity review can actually entail¹².

Subsidiarity Stripped: Reasoning without Escape

A remedy entrusted to national parliaments but deprived of any meaningful object of review would risk becoming little more than a symbolic annex to the Early Warning Mechanism. The more rigorously subsidiarity is separated from conferral, proportionality and national identity, the greater becomes the need to identify a judicial standard capable of operating within the constitutional space that remains. The Opinion does not provide an explicit answer. Yet it provides the premises from which one may be derived – and those premises point, with some consistency, in a single direction.

Throughout her analysis, AG Ćapeta consistently rejects any understanding of subsidiarity that would require the Court to determine whether Union action was substantively preferable to national action. The allocation of regulatory authority between different levels of governance remains a matter characterised by political discretion, predictive judgement and institutional choice. No standard of judicial review that required the Court to substitute its assessment for that of the legislature on this question could survive the objection that it transforms the Court into an arbiter of the optimal distribution of legislative authority within the Union.

The consequence, however, is not the disappearance of judicial review. It is its relocation. Once the substantive correctness of the legislative choice is removed from the centre of the analysis, judicial scrutiny can only focus on the reasons advanced in support of that choice. The constitutional question ceases to be whether the legislature was right to act at Union level and becomes whether it adequately explained why Union action was considered necessary. Judicial review of subsidiarity has often failed not because subsidiarity is inherently non-justiciable, but because scrutiny has been directed towards the wrong constitutional question¹³. Once the Court asks whether Union action was in fact preferable to national action, subsidiarity collapses into a political assessment. Once it asks whether the institutions have adequately justified that conclusion, subsidiarity becomes reviewable without becoming political. This shift is not without foundation in the existing constitutional architecture. The principle has progressively undergone a process of proceduralisation since Maastricht and, more visibly, since Lisbon. Legislative proposals must contain subsidiarity statements; impact assessments must address subsidiarity concerns; national parliaments are invited to evaluate the reasons supporting Union intervention and may challenge their adequacy through reasoned opinions. The constitutional architecture established by Protocol No 2 rests upon a simple premise: subsidiarity must be justified.

What remained comparatively underdeveloped was the judicial dimension of that obligation. Legislative recitals routinely state that Member States would be unable to achieve the objectives pursued and that Union action would be more effective – yet they frequently stop at assertion. The justificatory structure risks becoming circular: Union action is necessary because Union action has been chosen; Union action has been chosen because it is necessary¹⁴.

AG Ćapeta’s Opinion is particularly sensitive to this difficulty. At paragraph 136, the Opinion insists that subsidiarity reasoning cannot be formulaic: the institutions must provide a justification tailored to the specific characteristics of the measure under review, capable of enabling both political actors and the Court to understand why Union-level action is constitutionally warranted in the circumstances of the particular case¹⁵. That is a demanding standard, and its formulation is among the most valuable contributions of the Opinion.

Yet at paragraph 147, the Opinion accepts justifications that are, in significant part, generic recitations of the Art. 5(3) TEU formula supplemented by contextual references in paragraph 146¹⁶. The tension between these two paragraphs is not incidental. It marks precisely the boundary between what the Opinion achieves and what it leaves for the Court to resolve. Without criteria identifying what makes a subsidiarity justification adequate – what distinguishes a genuinely tailored justification from a sophisticated formula – the insistence on specificity risks remaining aspirational.

The doctrinal resources for resolving that tension are not absent from Union law. Across several areas, judicial review already operates through scrutiny of reasons rather than substitution of judgment. The case law concerning Art. 296 TFEU provides the most direct analogy: the Court does not substitute its assessment of whether a measure is appropriate; it examines whether the legislature provided reasons capable of demonstrating that it is¹⁷. A review of subsidiarity reasoning could follow the same logic without altering the constitutional balance established by the Treaties¹⁸. The relevant concept is reasonableness of justification: not whether Union action was reasonable, but whether the reasons offered for it were. A justification is adequate when it is sufficiently specific to the regulatory context at issue – when it explains, with reference to the concrete characteristics of the sector and the measure, why the objectives pursued could not have been comparably achieved at national level. Generality is not a vice in itself; it becomes one when it renders the justification indistinguishable from any other¹⁹. A review of subsidiarity reasoning of this kind preserves political discretion while avoiding judicial abstention. It respects the premise that decisions concerning the allocation of authority are primarily legislative and political. The legislature remains free to choose. It is not free to choose without explanation.

That obligation to justify does not float free of the broader constitutional architecture of the Union legal order. A justification requirement that remains purely aspirational — satisfied by formula rather than by reasoning — is incompatible with the autonomy²⁰ of a legal order that claims to govern the exercise of public authority through law rather than through discretion alone. To permit circular subsidiarity reasoning is, in constitutional terms, to permit the exercise of Union competence without genuine legal constraint: a result that the autonomous character of the Union legal order cannot accommodate without undermining its own foundations. The connection with the rule of law reinforces the same conclusion by a different route. The rule of law, as a foundational value of the Union under Art. 2 TEU and a structural principle of its institutional architecture, requires that the exercise of public power be subject to effective legal review²¹. That requirement is not satisfied by review that is nominally available but substantively empty²². A subsidiarity assessment that cannot be meaningfully scrutinised because it provides no reasoned basis for scrutiny is not a legal constraint on legislative discretion; it is its simulacrum. The transition from subsidiarity review to review of subsidiarity reasoning is therefore not merely a refinement of judicial technique. It is a condition of constitutional integrity — the minimum required to ensure that subsidiarity operates as a genuine legal principle rather than as a declaration of intent periodically reproduced in legislative recitals.

Conclusion: Seventeen Years on, over to the Court

The constitutional legacy of Case C-553/24 will be determined less by the judgment ultimately delivered than by the conceptual foundations laid in the Opinion of Advocate General Ćapeta. Those foundations are more consequential than the immediate procedural outcome might suggest.

Three contributions are of potentially lasting significance. The first is the reconstruction of Art. 8 Protocol No 2 as a sui generis constitutional remedy – a reconstruction that provides the institutional licence for a jurisprudence specifically calibrated to the function of subsidiarity litigation rather than derived by analogy from ordinary annulment proceedings. The second is the strategy of judicial containment, through which the admissibility perimeter of the Art. 8 action is defined with constitutional precision, separating subsidiarity from conferral, proportionality and national identity in a manner that preserves the conceptual integrity of each principle while preventing the parliamentary action from evolving into a general vehicle for contesting the distribution of legislative power within the Union. The third contribution, and the most significant for the long-term development of the Court’s subsidiarity jurisprudence, is the insistence that subsidiarity reasoning must be specific, tailored and reviewable – an insistence that carries as its necessary corollary the premise that the Court possesses both the licence and the responsibility to examine whether the justifications provided by Union institutions satisfy a standard more demanding than the formulaic reproduction of Art. 5(3) TEU.

Whether the Court will seize that opportunity in its judgment remains uncertain. The pressures toward minimalism are familiar: institutional deference, the sensitivity of migration as a policy domain, and the residual anxiety about judicial intrusion into legislative choices that runs beneath much of the Court’s subsidiarity jurisprudence. The transition from subsidiarity review to review of subsidiarity reasoning would require the Court to depart from that pattern – not by expanding the scope of review, but by applying with greater rigour the standard it nominally already applies. What the Opinion ensures is that those pressures can no longer operate invisibly. By reconstructing Art. 8 as a sui generis remedy and insisting on the need for tailored justification, AG Ćapeta has made explicit a constitutional commitment that the Court cannot simply disregard: that subsidiarity reasoning must be reviewable, and that reviewability must mean something.

There is, finally, a structural difficulty that no single judgment can fully resolve. The adequacy of subsidiarity reasoning depends in part on the quality of the legislative process that generates it. If impact assessments address subsidiarity only perfunctorily, the material available for judicial review will remain thin regardless of the standard applied. Yet the difficulty may lie not only with the institutions whose acts are reviewed, but also with the mechanisms designed to trigger and enrich subsidiarity scrutiny. More than fifteen years after Lisbon, the use of the Early Warning Mechanism remains comparatively modest²³. The number of reasoned opinions issued by national parliaments has never represented more than a small fraction of the legislative proposals transmitted to them and, after an initial period of greater activity, has generally declined. A similar trend can be observed in the broader political dialogue between national parliaments and the Commission. The relative scarcity of subsidiarity litigation may therefore reflect not only the limits of institutional responsiveness, but also the limited mobilisation of the parliamentary safeguards established by Protocol No 2. Significantly, the first action ever brought by a national parliament under Art. 8 of Protocol No 2 emerged not from a particularly intensive activation of the Early Warning Mechanism, but despite its generally limited use. The future effectiveness of subsidiarity review may therefore depend as much on the willingness of national parliaments to deploy the instruments conferred upon them by the Treaties as on the intensity of judicial scrutiny itself. The procedural and judicial dimensions of subsidiarity enforcement are thus connected in a deeper sense: a more demanding standard of review creates incentives for more careful upstream reasoning, but only if parliamentary actors continue to generate the objections, arguments and justificatory exchanges upon which meaningful review ultimately depends.

AG Ćapeta’s Opinion identifies with precision the constitutional terrain on which the future of Art. 8 will be decided. The question raised by Case C-553/24 is no longer whether subsidiarity is judicially enforceable. Lisbon settled that question in principle. The question is whether subsidiarity can become judicially meaningful. AG Ćapeta’s Opinion does not answer it. It merely creates the conditions under which the Court finally might transforming it from a principle of constitutional aspiration into a principle of constitutional justification.

¹ Opinion of Advocate General Ćapeta, 4 June 2026, Case C-553/24, Assemblée nationale de la République française v Parliament and Council (hereinafter ‘AG Opinion’).

² Protocol No 2 on the Application of the Principles of Subsidiarity and Proportionality OJ, C 115 of 9 May 2008, 206/209, Art 8.

³ Regulation (EU) 2024/1351 of the European Parliament and of the Council of 14 May 2024 on asylum and migration management, amending Regulations (EU) 2021/1147 and (EU) 2021/1060 and repealing Regulation (EU) No 604/2013, OJEU, L 1351 of 22 May 2024.

⁴ P. Kiiver, The Early Warning System for the Principle of Subsidiarity. Constitutional Theory and Empirical Reality, London, 2012, p. 141 ff.; K. Granat, The Principle of Subsidiarity and its Enforcement in the EU Legal Order. The Role of National Parliaments in the Early Warning System, Oxford, 2018, p. 159 ff.

⁵ AG Opinion, cit., points 55-63. For the lex specialis characterisation see P. Kiiver, op. cit., p. 46; R Schütze, European Constitutional Law, Cambridge, 2015, p. 278 ff.; and for an early scepticism toward that characterisation and an anticipation of the autonomous function of the Art. 8 remedy see A. Biondi, Subsidiarity in the Courtroom, in A. Biondi, P. Eeckhout, S. Ripley (eds.), EU Law after Lisbon, Oxford, 2012, p. 61 ff.

⁶ The parliamentary subsidiarity action cannot be reduced to a variation of a remedy from which its applicants are otherwise entirely absent: A. Cygan, Accountability, Parliamentarism and Transparency in the EU, 2013, p. 161 ff.

⁷ AG Opinion, cit., points 47-53. See K. Lenaerts, I. Maselis, K. Gutman, EU Procedural Law, Oxford, 2024, p. 92 ff.

⁸ AG Opinion, points 101-118; Court of Justice, 5 October 2000, Case C-376/98, Germany v Parliament and Council (Tobacco Advertising I), paras 83-88; 16 February 2022, Case C-156/21, Hungary v Parliament and Council, paras 232-240.

⁹ See A. Biondi, Subsidiarity in the Courtroom, in A. Biondi, P. Eeckhout, S. Ripley (eds.), op. cit., p. 61 ff.; E. De Capitani, Subsidiarity Control of European Rules also Open to Minorities in (Some) National Parliaments: What Consequences?, in Rivista del Contenziooso Europeo, 2024, p. 199 ff.

¹⁰ On subsidiarity as federal proportionality see R. Schütze, Subsidiarity after Lisbon: Reinforcing the Safeguards of Federalism?, in Cambridge Law Journal, 2009, p. 525 ff., pp. 533-538; G. Davies, Subsidiarity as a Method of Policy Centralisation, in A. Biondi, P. Eeckhout, S. Ripley (eds.), EU Law after Lisbon, Oxford, 2012, p. 280 ff.

¹¹ J.H.H. Weiler, The Transformation of Europe, in Yale Law Journal, 1991, p. 2403 ff., pp. 2483-2488; A. Stone Sweet, The Judicial Construction of Europe, Oxford, 2004, p. 54 ff.

¹² That difficulty is not new. It prompted G. T. Davies, Subsidiarity: The Wrong Idea, in the Wrong Place, at the Wrong Time, in Common Market Law Review, 2006, p. 63 ff., pp. 64-72, to argue that subsidiarity was a principle too politically indeterminate to sustain judicial enforcement without transforming the Court into an arbiter of legislative preference – a scepticism that finds earlier doctrinal roots in A. Estella, The EU Principle of Subsidiarity and its Critique, Oxford, 2002, p. 169 ff. The strategy of judicial containment adopted by AG Ćapeta can be read, in part, as a response to precisely that objection: by severing subsidiarity from conferral, proportionality and national identity, the Opinion attempts to carve out a residual core that is legally manageable without being politically intrusive. A procedurally-grounded response to that scepticism had already been anticipated in A Biondi, Subsidiarity in the Courtroom, in A. Biondi, P. Eeckhout, S. Ripley (eds.), op. cit., pp. 61-78; the Opinion of AG Ćapeta provides, for the first time, its judicial foundation.

¹³ See G. Davies, Subsidiarity as a Method of Policy Centralisation, in A. Biondi, P. Eeckhout, S. Ripley (eds.), op. cit., p. 280 ff.

¹⁴ F. Ippolito, Fondamento, attuazione e controllo del principio di sussidiarietà nel diritto della Comunità e dell’Unione europea, Milano, 2007.

¹⁵ AG Opinion, cit., point 136.

¹⁶ AG Opinion, cit., point 147.

¹⁷ Art. 296 TFEU; Court of Justice, 27 June 2006, Case C-540/03, Parliament v Council, para. 75; 22 December 2010, Case C-77/09, Gowan Comércio Internacional, para. 57. On the duty to state reasons as a standard of constitutional accountability see P. Craig, EU Administrative Law, Oxford, 2018, p. 371 ff.

¹⁸ The possibility of a procedurally-oriented subsidiarity review, focused on the adequacy of reasoning rather than the correctness of legislative choices, had been anticipated in the literature: F. Ippolito, op. cit.; A Biondi, Subsidiarity in the Courtroom, in A. Biondi, P. Eeckhout, S. Ripley (eds.), op. cit., pp. 74-76. The Opinion of AG Ćapeta provides, for the first time, a judicial foundation for that possibility.

¹⁹ The analogy with proportionality review is instructive. The Court does not substitute its assessment of whether a measure is proportionate; it examines whether the legislature provided reasons capable of demonstrating proportionality. The same logic is available for subsidiarity: G. de Búrca, The Principle of Subsidiarity and the Court of Justice as an Institutional Actor, in Journal of Common Market Studies, 1998, p. 217 ff., pp. 231-233.

²⁰ On the principle of autonomy see K. Lenaerts, The Autonomy of European Union Law, in Il Diritto dell’Unione europea, 2018, p. 617 ff.; L. Lionello, L’autonomia dell’ordinamento giuridico dell’Unione Europea. Significato, portata e resistenze alla sua applicazione, Torino, 2024.

²¹ Art. 2 TEU; Court of Justice, 27 February 2018, Case C-64/16, Associação Sindical dos Juízes Portugueses, para. 32; 24 June 2019, Case C-619/18, Commission v Poland, paras 42-48.

²² On the rule of law as a justiciable principle within the Union constitutional order see D. Kochenov, EU Enlargement and the Failure of Conditionality: Pre-accession Conditionality in the Fields of Democracy and the Rule of Law, The Hague, 2008, p. 3 ff.; L. Pech, K. Scheppele, Illiberalism Within: Rule of Law Backsliding in the EU, in Cambridge Yearbook of European Legal Studies, 2017, p. 3 ff., pp. 7-14.

²³ The Commission’s annual reports indicate a significant reduction in the volume of parliamentary contributions submitted both under the subsidiarity control mechanism and through the political dialogue from 2011 to nowadays. See especially, European Commission, Annual Report 2024 on the application of the principles of subsidiarity and proportionality and on relations with national Parliaments, 8 September 2025, COM(2025) 473, pp. 9-11 and D. Fromage, Subsidiarity, proportionality and the role of the national parliaments in the European legislative process, European Parliament Study update, April 2025, available at the following link https://www.europarl.europa.eu/RegData/etudes/STUD/2025/773579/IUST_STU(2025)773579_EN.pdf (last accessed 18th June 2026); F. Fabbrini, K. Granat,  Yellow Card, But No Foul: The Role of the National Parliaments under the Subsidiarity Protocol and the Commission Proposal for an EU Regulation on the Right to Strike, in Common Market Law Review, 2013, p. 115 ff.; I. Cooper, National Parliaments in the Democratic Politics of the EU: the Subsidiarity Early Warning Mechanism, 2009-2017, in Comparative European Politics, 2019, p. 919 ff.; T. Jaroszyński, National Parliaments Scrutiny of the Principle of Subsidiarity: Reasoned Opinions 2014-2019, in European Constitutional Law Review, 2020, p. 91 ff.