59It is settled case-law that, by virtue of the principle of primacy of EU law, which is an essential feature of the EU legal order (see Opinion 1/91 [1991] ECR I-6079, paragraph 21, and Opinion 1/09 [2011] ECR I-1137, paragraph 65), rules of national law, even of a constitutional order, cannot be allowed to undermine the effectiveness of EU law on the territory of that State (see, to that effect, inter alia, Case 11/70 Internationale Handelsgesellschaft [1970] ECR 1125, paragraph 3, and Case C-409/06 Winner Wetten [2010] ECR I-8015, paragraph 61).
Source: EUR-Lex, © European Union, 1998-2026. Reuse authorised under Decision 2011/833/EU.