Does the power of international courts strengthen or threaten national judicial systems? Examining how EU member states navigate tensions between domestic rule of law and ECJ rulings.

Introduction: This article explores whether European Union law influences domestic constitutional review through the lens of separation-of-powers politics.

Data & Methods: Using comparative analysis across fifteen EU nations, we track legislative responses to landmark judgments from the European Court of Justice over two decades.

Key Findings: National parliaments increasingly reject ECJ interpretations despite legal obligation—Spain stands out as an exception due to its institutional design.

Why It Matters: This nuanced finding suggests domestic political contexts shape compliance with international judicial decisions, challenging assumptions about court effectiveness and sovereignty dynamics.