Abstract
In order to enter the Banking Union, non-euro EU Member States must ‘step outside’ the EU legal order and the Union’s institutional framework, and resort to unilateral instruments of public international law. If the intergovernmental method has advanced the alternative project of integration based on voluntary policy, international unilateralism is seen as a similar integration technique based on the voluntary action of non-euro Member States, ie a tool for deeper integration that appears as a variation of intergovernmentalism. This article focuses on the constitutional deficiencies caused by the choice of unilateral instruments in the institutional set-up of a close cooperation arrangement in the Single Supervisory Mechanism. At first sight, leaving the EU legal order and entering the world of international law opens entirely new perspectives for the participating Member States. The possible attraction is escaping the constraining institutional framework of EU law. However, the international law route poses significant constitutional challenges vis-à-vis compatibility with the EU law.