In the European Union, the ne bis in idem principle restricts the ability of EU and national enforcement authorities to prosecute or punish the same defendant for the same criminal offence more than once. That protection applies to competition fines due to its punitive and deterrent natures and their high degree of severity. In reviewing the ECJ jurisprudence, the article traces back the justification of the case law on the irrelevance of the legal interest protected as necessary requirement for the proper application of the ne bis in idem principle to specific situations where there was a duplication of penalty proceedings for formally distinct but materially overlapping offences, imputable the generalized lack of harmonization of penalty rules in the EU. The article argues that, in the area of EU competition law however, the unity of the legal interest is still a necessary requirement to apply the protection conferred by that principle. This is because, under the harmonized system of competition enforcement in the EU, unlike in other areas of EU law, the Commission and the national competition authorities share concurring competences on a clear differentiation based on the notion of affectation of EU trade, which makes the legal interest protected the critical element of the notion of same infringement.
It follows that the Commission and the national authorities can deal with separate aspects of a same anti-competitive material conduct by pursuing separate offences corresponding to different legal interests protected. Moreover, competition is a horizontal discipline that has general application in all areas of the economy and intersects with sectoral regulations. This entails that concurrent proceedings to sanction materially different offences other than competition are possible without this infringing the non bis in idem protection. An illustration of this can be found in the area of the new economy where a competition infringement can be based on the abuse of data collected in violation of privacy rules. A same material practice based on inappropriate handling of data by an internet platform could well constitute at the same time an anti-competitive abuse and violate data protection rules, which should be pursed as separate offences. Disregarding the interest protected would lead to sacrificing one interest over another and lead the authorities into unacceptable choices in pursuing offences.