An action for annulment under Article 263 TFEU must be available in the case of all measures adopted by the EU institutions, irrespective of their nature or form, provided that they are intended to have legal effects. A decision of the Council and of the Representatives of the Governments of the Member States on the signing, on behalf of the European Union, of an agreement under which third States accede to an international agreement concluded by the European Union and of an ancillary agreement, and on the provisional application of those agreements by, first, the European Union and, second, the Member States, must be regarded as an act of the Council against which an action for annulment may be brought, since the Council has participated in the decisions made in respect of all of those matters.

As provided in Article 13(2) TEU, each institution must act within the limits of the powers conferred on it by the Treaties, and in conformity with the procedures, conditions and objectives set out in them. The rules regarding the manner in which the EU institutions arrive at their decisions are laid down in the Treaties and are not at the disposal of the Member States or of the institutions themselves.

In the case of a decision authorising the signing of an agreement between the European Union and third States or international organisations and, if necessary, its provisional application by the European Union, under Article 218(5) TFEU no competence is granted to the Member States as the decision must be adopted by the Council. Accordingly, it is necessary to annul a decision of the Council and of the Representatives of the Governments of the Member States, authorising the signing of a mixed agreement on behalf of the European Union and providing for its provisional application, which in fact merges two different acts, namely, on the one hand, an act relating to the signing of that agreement on behalf of the European Union and its provisional application by the latter and, on the other, an act relating to the provisional application of the agreement by the Member States, without it being possible to discern which act reflects the will of the Council and which the will of the Member States. In so doing, the Council has been involved, as an EU institution, in the adoption of the act concerning the provisional application of a mixed agreement by the Member States although such an act falls within the scope of, first of all, the internal law of each of those States and, then, international law. Moreover, since Article 218(8) TFEU provides that the Council must act, on behalf of the European Union, by a qualified majority, the two different acts, brought together in that decision, cannot be validly adopted under a single procedure. The act concerning the provisional application of a mixed agreement by the Member States entails consensus of the representatives of those States, and therefore their unanimous agreement.

Furthermore, whilst it is true that in the field of mixed agreements it is essential to ensure close cooperation between the Member States and the EU institutions, both in the process of negotiation and conclusion and in the fulfilment of the commitments entered into, that principle cannot, however, justify the Council setting itself free from compliance with the procedural rules and voting arrangements laid down in Article 218 TFEU.

(see paras 41, 42, 44, 48-50, 52, 54, 55)