The recent judgment in the case of Puigdemont i Casamajó and Others v Parliament (C-572/23 P) stems from the 2017 Catalan independence referendum and the subsequent efforts by the Spanish Supreme Court to prosecute former Catalan President Carles Puigdemont for sedition and misuse of public funds. Back then, Puigdemont was a sitting member of the European Parliament and the Spanish Supreme Court asked to waive his parliamentary immunity. The legal battle became highly controversial because it forced the European Parliament to navigate the tension between national sovereignty (Spain's right to enforce its laws) and the protection of European parliamentary independence. On the European level, the dispute shifted from the underlying criminal charges to whether the European Parliament’s internal process for waiving immunity was biased, raising fundamental questions about the right to an impartial hearing within EU institutions and the rule of law.

It is notably professed, acknowledged, and normatively accommodated that the principle of the Rule of Law is a founding value of the European Union (Article 2 TEU) and, in my view, the most singular (material) constitutional trait of the EU’s constitutional identity. The strength of this assertion is unmistakably reflected in the central normative status of the principle within the constitutional architecture of the Union, where it operates not merely as a foundational value under Article 2 TEU but as a structural premise supporting the autonomy, coherence, and effectiveness of EU law. Its significance is further evidenced by the vast body of European rule-of-law provisions, spanning primary law, secondary legislation, soft-law instruments, and conditionality mechanisms designed to secure compliance by the Member States. The copious academic output devoted to the principle likewise attests to its doctrinal richness and contested evolution, engaging questions of judicial independence, separation of powers, mutual trust, and the limits of supranational oversight. Finally, the profound political and institutional impact of the CJEU’s case law — particularly in its articulation of judicial independence as an essential component of effective judicial protection under Articles 19(1) TEU, 47 CFR, and 2 TEU — demonstrates how the principle has evolved from a declaratory value into an enforceable constitutional standard.

One of the implicit dimensions of the principle of the rule of law is the separation of powers and the system of checks and balances among institutions — in the present context, among the institutions of the Union. As recently highlighted by Regulation (EU) 2020/2092 (the Conditionality Regulation), the principle of separation of powers constitutes a fundamental component of the rule of law, reflecting the values common to the Member States as enshrined in Article 2 TEU. In this sense, the rule of law not only requires judicial independence and effective judicial protection, but also presupposes a structured institutional equilibrium in which each Union institution acts within the limits of its competences while remaining subject to the legal and political accountability mechanisms inherent in the EU constitutional framework.

This institutional dimension of the rule of law — grounded in separation of powers and mutual checks among Union institutions — is further illustrated by the Court’s judgment in Case C-572/23 P, Puigdemont i Casamajó and Others v Parliament. In that case, the Court of Justice set aside the judgment of the General Court and annulled the European Parliament’s decisions to waive the parliamentary immunity of several Members. The annulment was not based on the substance of the criminal allegations pending at national level, but on procedural guarantees linked to impartiality. The Court held that the appointment of the rapporteur responsible for examining the requests for waiver failed to satisfy the requirement of objective impartiality, given that the rapporteur belonged to the same political group as Members of the political party that had initiated the criminal proceedings at national level (the Spanish Vox party). By clarifying that such circumstances are capable of giving rise to legitimate doubts as to impartiality — and that Parliament must organise its internal procedures accordingly — the Court reaffirmed the centrality of good administration and institutional neutrality within the EU constitutional framework.

The judgment may thus be understood as a concrete manifestation of the systemic checks and balances inherent in the rule of law as enshrined in Article 2 TEU. Through judicial review, the Court ensured that Parliament exercised its prerogatives within the limits imposed by principles of impartiality and sound administration. In doing so, it did not encroach upon Parliament’s political discretion, but rather corrected a procedural deficiency affecting the integrity of the decision-making process. In my understanding, the ruling therefore exemplifies how the separation of powers operates within the Union: the Court, acting within its constitutional mandate, reviews and, where necessary, rectifies the acts of another institution, thereby safeguarding institutional equilibrium and reinforcing the normative substance of the rule of law.

The corrective intervention of the Court was expressed in clear and unequivocal terms, as it explicitly found that the guarantees of objective impartiality required in the appointment of the rapporteur had not been satisfied. In this respect, the judgment constitutes an important institutional clarification directed at the European Parliament, particularly in a context in which the handling of requests for the waiver of parliamentary immunity has attracted heightened legal and political attention. The ruling may therefore be seen as an opportunity for institutional refinement. The European Parliament may wish to reflect upon this decision with a view to reinforcing internal procedural safeguards so as to minimise the risk of similar concerns arising in future cases, especially in politically sensitive matters. More broadly, the case highlights the importance of adopting and consistently applying mechanisms that ensure objective impartiality in proceedings affecting Members’ status. Irrespective of one’s political assessment of the individuals concerned or of the broader national context, the essence of the rule of law lies precisely in requiring that institutional decisions comply with standards of legality, neutrality, and procedural fairness.