This article considers the implications of the European Commission, as primary administrative enforcer of competition law in the Union, using its own ‘preliminary reference procedure’, through observations in national court proceedings under Council Regulation 1/2003, to minimise the risks of divergent application of EU anti-trust rules under the decentralised system of enforcement ushered in by that Regulation. It sets the scene with the relationship between the European Commission and national courts in competition law, before describing the relevant provisions of the Regulation and its accompanying Courts Notice. It then discusses the legal nature of the Commission opinion as a Union instrument. Identifying cases where the Commission has offered observations, it assesses the implications of administrative intervention in judicial decision making. It finds that greater transparency is crucial for legitimacy, legal certainty and maximum impact on consistent application.