49First of all, in conformity with the principles of international law, European Union institutions which have power to negotiate and conclude an international agreement are free to agree with the third States concerned what effect the provisions of the agreement are to have in the internal legal order of the contracting parties. Only if that question has not been settled by the agreement does it fall to be decided by the courts having jurisdiction in the matter, and in particular by the Court of Justice, in the same manner as any question of interpretation relating to the application of the agreement in the European Union (see Case 104/81 Kupferberg [1982] ECR 3641, paragraph 17, and Case C-149/96 Portugal v Council [1999] ECR I-8395, paragraph 34).
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