The Lisbon Treaty is silent about the principle of the supremacy of the European Union law over national law. However, Declaration number 17 was attached to the aforementioned Treaty to this effect. There can be seen a very unambiguous perspective on the issue of supremacy of European Union law over disagreeing national law: ‘under the principle of supremacy, precedence must always be given to Community law over conflicting national law however framed and including national constitutional provisions'.
As it is firmly known, the discussed principle of supremacy was established as well as developed in almost historical case of Costa v. Enel. In that case the collision between the law of the European Community and the Italian national law had been analysed. The conclusion of the European Court of Justice (hereinafter referred to as ‘ECJ') was based upon the limitation of sovereignty of each Member State and also on the transfer of powers from the States to the Community. The ECJ's core justifications for the discussed principle are ‘independence, uniformity and efficacy' of Community law. From this point of view, European Union law is ‘an integral part of ... the legal order applicable in the territory of each of the Member States'.
The ECJ has developed arguments that would validate the conclusion about the Community law being accorded supremacy over national law. Undoubtedly, integration and co-operation were the crucial aims of the Treaty. They might be destabilised by one Member State which refuses to give effect to the Union law that should equally bind all. Therefore, in Costa the Court did seek to establish a universal principle of the supremacy of all binding Union law.
The aforementioned case stands for the conceptual basis of the supremacy of the EU law since the strength and, evidently, scope of it were developed in later decisions. The subsequent case provides that the legal status of an inconsistent national measure were