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By its landmark ruling on 6 March 2018 in the Achmea case, the European Court of Justice considered that ISDS in an international agreement between EU Member States, such as an intra-EU bilateral investment treaty (BIT), can have an adverse effect on the autonomy of the EU legal order because investment tribunals can decide matters of EU law without being under the Court’s control. Specifically, the Court ruled that if a tribunal is called on to resolve a dispute liable to relate to the interpretation or application of EU law, its decisions must be subject to mechanisms capable of ensuring the full effectiveness of EU law. For this purpose, either the arbitral tribunal must constitute a court or tribunal situated within the judicial system of the EU, or its arbitral awards must be subject to judicial review by such court or tribunal, so that in either case questions of EU law which the arbitral tribunal may have to address can ultimately be submitted to the Court by means of a reference for a preliminary ruling. Since neither of these conditions were present with respect to the ISDS provision at issue—and normally would not be in other intra-EU BITs either—the Court ruled that the ISDS provision was incompatible with EU law.