Esin Kucuk, Lecturer in EU Law, University of Essex

Over the past decade, there has been a remarkable transformation towards the judicialisation of solidarity, characterized by the Court of Justice’s decision-making extending beyond the traditional boundaries of judicial authority. This trend has been propelled by a complex and multifaceted set of influences. For instance, it can be largely attributed to the increased emphasis on solidarity in various EU Treaty provisions [A1] following the Lisbon amendments. This includes provisions such as Article 2 of the TEU, which sets out the fundamental values of the EU and identifies solidarity as a key element of European society, as well as Article 3 TEU, which calls for solidarity among Member States as a goal of the Union. Additionally, the Treaties require both the Member States and the EU to maintain solidarity in a number of specific policy areas. This encompasses Article 80 TFEU concerning asylum, immigration, and border control, Article 122 TFEU in relation to emergencies and crises, Article 194 TFEU on energy matters, and Articles 222 TFEU and 42(7) TEU regarding security policy.

The above EU treaty provisions are undoubtedly significant, yet they do not fully account for the depth and frequency of the judicialisation of solidarity. The period following the Lisbon Treaty saw only a tepid engagement with the principle, despite the Treaty’s clear emphasis on solidarity, which suggests the influence of other, more compelling factors. Important among these has been a succession of crises, which have provided a conducive environment for the judicialisation of solidarity. Judicialisation has been further intensified by the growing body of EU secondary legislation aimed at implementing solidarity in areas particularly affected by crises, such as asylum and energy[A2] [A3] . This legislative growth has been crucial, not only in expanding the legal framework but also in actively influencing the judicial landscape. 

Another significant factor has been the marked increase in the number of claims that are built on solidarity as a ground for judicial review, a recent example being Case C-675/22 Poland v. Council. [A4] [A5]  This pending case concerns the legality of a new Regulation establishing rules concerning voluntary and mandatory demand-reduction targets for gas consumption. The applicant argues that the Regulation infringes, inter alia, the principle of energy solidarity as set out under Article 194 TFEU. The interesting aspect of this case is that both the contested legislation and the request for its annulment are grounded in solidarity.

However, the key element in the development of solidarity as a constitutional principle has been the Court of Justice’s increasing readiness to engage with it. In tracing the evolving normative force of the principle of solidarity within European jurisprudence, in my view, three critical junctures are particularly noteworthy.[A6] [A7] [A8] 

i. Solidarity as a legality standard

In the unfolding narrative of European jurisprudence, the Case T‑883/16 Opal v. Commission (Opal case) stands as a notable landmark, as this was the first case where solidarity served as a legality standard. Here, the General Court engaged in a significant act of judicial review, annulling a Commission decision on the grounds of contravening the principle of energy solidarity, as enshrined in Article 194 TFEU (paras. 79-85). 

It is important to note that the full potential of solidarity as a justiciable principle remains untested. Firstly, the extent to which this principle can serve as a benchmark in the review of legislative acts has yet to be seen. The Opal case opens the door to this possibility, but the depth and breadth of its application as precedent merits clarification in future jurisprudence. Secondly, while the General Court demonstrated a willingness to use the principle of solidarity as a yardstick in the context of energy, it notably restricted its scrutiny to procedural aspects. 

It is also noteworthy that the General Court, subtly yet decisively, shifted the perspective from a collective ‘one for all’ doctrine to an ‘all for one’ perspective. [A9] [A10]  Traditionally, solidarity as a principle of EU law had been primarily employed to underpin EU measures [A11] that required Member States to make concessions for the collective benefit of the Union. The reasoning of the Court in the Opal case, however, marks a departure from this trend, indicating that the EU’s common interest does not always prevail. This implies that even when a measure is in the EU’s general interest, the principle of solidarity might permit the interests of an individual Member State to take priority. This wider approach underpins the Court’s rationale for the annulment, which revolved around a failure to balance properly the individual interests of the applicant state against the broader interests of the European Union (paras. 77, 82). This reorientation in the Court’s approach is not merely a minor adjustment but a significant stride in the judicial development of the principle of solidarity. 

ii. Member State solidarity as a general principle of EU law

Equally significant is the General Court’s reference to solidarity between the Member States as a general principle of EU law (para. 69). Although this general principle has not yet served as the foundation for a legal claim, its potential normative force should not be underestimated. As mentioned earlier, solidarity is extensively codified in the Treaty across various domains. On the other hand, while there is no explicit mention of solidarity at the Treaty level in some areas, such as environmental protection, the [A12] relevance of the principle is undeniably underscored by recently introduced schemes.[A13]  For instance, the European Climate Law, which mandates Member States to achieve climate neutrality, and Directive 2018/410, focusing on emission reductions, both heavily draw on solidarity as the foundational rationale for the obligations they impose. This is despite the absence of an explicit requirement in the Treaty to act in solidarity per se. The general principle of solidarity may be instrumental in underpinning the legal validity of any act that imposes environmental protection obligations, even when such acts face challenges based on the principle of energy solidarity.[A14] 

iii. Solidarity as a fundamental principle of EU law

Perhaps the most crucial advancement in the justiciability of solidarity is its recognition as a fundamental principle [A15] [A16] by the Court of Justice (para. 38). On appeal in Opal, the Court of Justice upheld the General Court’s decision, but referred to solidarity as a fundamental principle. How does this differ from the General Court’s approach? The General Court’s acknowledgment of solidarity among the Member States as a general principle is undoubtedly a key development. However, it appears to deliberately circumvent a more expansive ambit of solidarity. Solidarity, as a fundamental principle, goes beyond mere Member State interactions and encompasses the broader social dimensions of solidarity, which are particularly evident in the context of interactions among EU citizens. The suggestion of the Court that solidarity, as a fundamental principle, underpins the entire EU legal system (para. 41) [A17] reflects its relevance also in social spheres within the Union.

It is important to highlight that this mention of solidarity as a fundamental principle is not an unprecedented move by the Court of Justice, as it has previously acknowledged that solidarity was a fundamental principle in the context of solidarity between different undertakings (para. 59). Additionally, the Court’s application of the concept of solidarity in social contexts, as seen in Case C-184/99 Grzelczyk (para. 44) without clear legislative support, reflects a broader application of this principle. However, the Court has been reluctant on occassion to use solidarity as a key interpretative tool. For instance, in Case C-370/12 Pringle, the Court could have applied solidarity to interpret the ‘no bail-out’ clause in Article 125 TFEU more restrictively, but chose not to. This cautious approach suggests that the principle of solidarity, while maturing, had not yet fully ripened. Telling is AG Kokott’s Opinion (paras.142-143), suggesting a narrow interpretation of Article 125 TFEU without acknowledging the status of solidarity as a principle, and consequent legal obligations attached to it, though clearly recognising its constitutional status and relevance. 

Conclusion

What then differentiates the current legal landscape post-Opal? There is an observable synergy in the advancement of solidarity, discernible in recent legal developments, most notably Next Generation EU. One can perhaps add to this the advances made in the New Pact on Migration and Asylum, in which solidarity plays a central role. Interpreting these developments as a natural consequence of a societal shift towards greater social integration and the formation of a shared common identity requires a mix of imaginative and, perhaps, optimistic thinking.

A more compelling explanation lies in the context in which solidarity is being reaffirmed as a fundamental principle. These instances are embedded within a broader legal framework that concerns the judicialisation of fundamental EU values and principles, particularly the rule of law (C-156/21  Hungary v Parliament and Council). The linkage of solidarity, fundamental principles, and values that are considered the backbone of the EU legal order is a clear manifestation of where the Court situates this principle within the EU legal order (para. 129). When seen from this perspective, the increasing normative force of solidarity may not be entirely surprising. Whether the elevation and broadening of the principle of solidarity heralds a beneficial transformation or ushers in new layers of complexity within the EU legal framework is a matter for future contemplation. However, it unmistakably signifies a pivotal moment in the development of European jurisprudence, positioning solidarity as a key concept in shaping the future of the EU legal order.

Some of the ideas shared in this blog are based on my recent article: ‘Solidarity in the EU: What Is In A Name?’(2023) 6(2) Nordic Journal of European Law, 1-28.

Esin is also currently working on a monograph entitled ‘European Integrated Border Management and Solidarity: The Limits of Protection Responsibility’ which will be published by Hart Publishing.

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