15 July 1964 | Costa/ENEL ruling. A groundbreaking case that established the principle of primacy of EU law over the laws of EU countries. Or how an unpaid electricity bill led to one of the key principles of EU law. #OnThisDay #EUHistory

The judgment concerned an Italian law which nationalised the production and distribution of electrical energy. Mr. Costa, in the course of a dispute over his electricity bill (1925 lire) invoked the incompatibility of this law with the EEC Treaty.

The Italian government claimed that national judge was required to apply Italian law, adopted after the Treaty, and could not challenge it before the EU Court. The EU Court rejected that interpretation by referring to the primacy of EU law.

"By contrast with ordinary international treaties, the EEC Treaty has created its own legal system which (...) (has become) an integral part of the legal systems of the Member States and which their courts are bound to apply"

The EU court sustained that the executive force of EU law cannot vary from one state to another in deference to subsequent domestic laws...without jeopardizing the objectives of the treaty or causing discrimination. The judgement here: