The starting point for this question is the Van Gend en Loos case:
'We must conclude from this that the [Union] constitutes a new legal order in international law, for whose benefit the States have limited their sovereign rights, albeit within limited fields, and the subjects of which comprise not only the member-States but also their nationals. [Union] law, therefore, apart from legislation by the member-States, not only imposes obligations on individuals but also confers on them legal rights. '