Arbitration — Arbitration between two Member States of European Union — Delimitation of maritime and land borders — Arbitration agreement breached — Arbitration agreement unilaterally terminated — Final arbitration award — Validity of arbitration award contested — Arbitration award not implemented — Relationship between arbitration agreement and European Union law — European Union not a party to arbitration agreement between Member States

Jurisdiction — Treaties — European Union — Jurisdiction of the Court of Justice of the European Union — Treaty on the Functioning of the European Union, 2007 — Article 259 — Alleged failure of Member State to fulfil obligations — Competence of the European Union in border dispute — Alleged infringements of EU law ancillary to alleged infringement of arbitration agreement — Relationship between European Union law and arbitration agreement and award

International tribunals — Arbitration agreement — International law governing arbitration agreement — Arbitration award — Relationship between arbitration agreement and arbitration award and European Union law — Obligations of Member States of the European Union — Accession to European Union — Arbitration agreement referred to in accession agreement — Validity of arbitration award contested — Competence of European Union in border dispute — Ratione materiae of European Union law with respect to international legal instruments

International organizations — European Union — Member States — Obligations of Member States of the European Union — Accession to European Union — Arbitration agreement referred to in accession agreement — Where validity of arbitration award contested — Arbitration award not implemented — European Union not party to arbitration agreement between Member States — Relationship between arbitration agreement and arbitration award and European Union law — Scope ratione materiae of EU law in relation to international legal instruments — Competence of European Union in border dispute

Territory — Sea — Slovenia — Croatia — Delimitation of land and sea borders — Power to determine territory retained by European Union Member States — Delimitation of borders contested — Arbitration award delimiting borders contested — Action would require determination of borders between two European Union Member States — The law of the European Union