Although the Lisbon Treaty recognises the necessity to limit the power of the European Union, some of its limitations are poorly expressed. As a result, the European Commission has the possibility to act arbitrarily by expanding Union power. The position of the Commission is pre-eminent, notably with respect to the drafting of EU measures. Not only can the Commission expand Union power, but it may also favour certain actors at the expense of the principals (Member States and their citizens). Indeed, the Commission may apply definitions of the ‘common European interest’ that go beyond the preferences of the principals.