On 6 March 2018, the Court of Justice of the European Union issued a long-awaited decision on a preliminary ruling on the Slovak Republic v Achmea case. 

 Original dispute between Achmea, one of the largest suppliers of financial services in the Netherlands, and Slovakia arose out in 2006 when Slovakia reversed liberalization of its health insurance market. In 2008, Achmea initiated arbitration proceedings against Slovakia under the bilateral investment treaty (BIT) concluded between the Netherlands and Slovakia. In 2012, in its final award, an arbitral tribunal constituted under the UNCITRAL found that Slovakia had violated the BIT and ordered it to pay EUR 22.1 million as compensation. Slovakia subsequently initiated the setting-aside proceedings before the Higher Regional Court of Frankfurt (the arbitral tribunal was seated in Frankfurt). Slovakia argued that the arbitral tribunal lacked jurisdiction to hear the claims because the arbitration clause was incompatible with EU law. Although the Higher Regional Court of Frankfurt rejected Slovakian argumentation, the German Federal Court of Justice hearing the case on appeal, referred questions on the compatibility with EU law of the BIT's arbitration clause to the CJEU for a preliminary ruling. 

The CJEU concluded that arbitration clause in intra-EU bilateral treaties is incompatible with EU law. In particular, the CJEU held that the mechanism for settling disputes between an investor and a host state is incompatible with the principle of autonomy of EU law as it is enshrined in Articles 344 and 267 of the Treaty on the Functioning of the EU (TFEU). 

The Court observed that the arbitration procedure is not itself capable of ensuring the uniform application of EU law. Since arbitral tribunal cannot be regarded as a 'court or tribunal', it is not entitled to make a reference to the Court for a preliminary ruling. Since arbitral award is subject only to limited judicial review by competent national courts, uniform and consistent interpretation of EU law is not ensured. 

 Overall, the Court found that Articles 267 and 344 TFEU must be interpreted as precluding a provision in an international agreement concluded between EU member states, under which an investor from one of those member states may, in the event of a dispute concerning investment in the other member state, bring proceedings against the latter member state before an arbitral tribunal.