European Union Agencies and Implementation: ACER's Authority in Effectuating a Contested EU Energy Rule

Abstract European Union (EU) agencies have increasingly been tasked with supporting the implementation of EU legislation, yet their impact on how such implementation unfolds remains understudied. Whilst existing research suggests that EU agencies can generally improve implementation outcomes, it offers limited insight into the impact that EU agencies have on how EU rules are implemented at the national level. This article examines how the work of an EU agency can shape the implementation of a specific EU rule. Focusing on the Agency for the Cooperation of Energy Regulators (ACER) and the 70% rule under EU electricity market regulation, we explore how ACER used its tasks to promote more uniform implementation across member states. Drawing on a qualitative case study, we show that ACER acted entrepreneurially – leveraging both formal and informal authority – to influence national implementation. Although it could not fully overcome national resistance, ACER contributed to greater convergence in implementation practices. The findings highlight how EU agencies can play an active role in shaping national implementation of EU rules, entailing more ‘multi‐level implementation’ in the EU. The article offers an analytical framework that may be applied to assess similar dynamics in other policy areas and agency contexts.