Article 23 TFEU

Every citizen of the Union shall, in the territory of a third country in which the Member State of which he is a national is not represented, be entitled to protection by the diplomatic or consular authorities of any Member State, on the same conditions as the nationals of that State. Member States shall adopt the necessary provisions and start the international negotiations required to secure this protection.

The Council, acting in accordance with a special legislative procedure and after consulting the European Parliament, may adopt directives establishing the coordination and cooperation measures necessary to facilitate such protection.