Authority Transfer and Politicised Member State Litigation before the Court of Justice of the EU

European integration is increasingly politicised. Contributing to a new strand of research that examines how EU institutions and Member State governments respond to this trend, this article focuses on the judicial arena. We explore whether authority transfers to the EU have provoked legal mobilisation by Member States before the Court of Justice of the EU, and we analyse the salience and polarisation of this litigation over time. Based on original data on interventions in all direct actions with government parties from 1954 to 2022, we find intensifying but differentiated judicial politicisation. Member States increasingly mobilise against European legislation, implementation, and enforcement. While challenges to legislation grew more salient but not more polarised over time, litigation against implementation decisions became more controversial but remained obscure. We argue that these varying trends mirror differential changes in the authority of EU institutions to enact, implement and enforce binding rules.