Achmea: When Investment Arbitration Collided with EU Autonomy

Abstract: This article examines the Court of Justice’s judgment in Achmea as a constitutional ruling on the autonomy of EU law rather than a narrow decision confined to a single arbitration clause. It reconstructs the Court’s reasoning in detail, contrasts it with Advocate General Wathelet’s more permissive Opinion, and explains why the judgment was widely understood to extend beyond the arbitration clause contained in the Netherlands-Slovakia BIT to similarly structured intra-EU investment treaties. The article also considers the broader institutional and legal response that followed Achmea, including the reaction of Member States and EU institutions, in order to situate the judgment within its wider systemic context. It argues that, while Achmea fundamentally altered the legal position of intra-EU BITs by linking their validity to the constitutional requirements of the EU judicial order, its implications for extra-EU BITs are more limited and depend on the specific treaty framework and the extent to which EU law is liable to be engaged.

• Introduction

What began as a dispute between a Dutch investor and Slovakia, then became a constitutional ruling on the limits of investor-State arbitration within the European Union.

In Achmea, the Court of Justice did more than invalidate the arbitration clause contained in an intra-EU bilateral investment treaty. It held, in substance, that disputes liable to require the interpretation or application of EU law cannot be conclusively entrusted to a body outside the judicial framework established by the Treaties. Achmea is therefore best understood not as a narrow ruling on one arbitral clause, but as a judgment on the autonomy of EU law and the integrity of the EU judicial system.

• Why Intra-EU BITs Became Problematic After Accession

Bilateral investment treaties (BITs) are international agreements designed to protect investments made by nationals or companies of one State in the territory of another. They typically contain substantive standards of protection, such as guarantees against unlawful expropriation, and often provide for investor-State arbitration as an alternative to proceedings before domestic courts.

Many of the BITs, that later became intra-EU BITs, were concluded in the late 1980s and 1990s between existing Member States and Central and Eastern European countries before the latter joined the European Union. Their purpose was to reassure investors entering transition markets by granting substantive protections and access to arbitration. Once those States acceded to the Union, however, those treaties became agreements between Member States, and their compatibility with EU law became increasingly contested. The objection was that, within the internal market, cross-border investment ought in principle to be governed by the common framework of EU law rather than by bilateral treaties granting asymmetric protections to investors of particular Member States.

That tension had already been identified before Achmea reached the Court of Justice. In a 2006 note, the Commission’s Directorate-General for the Internal Market and Services suggested that many provisions of intra-EU BITs had been superseded by EU law and that their legal status after accession was uncertain. In 2015, after most Member States had taken no action, the Commission increased pressure by initiating infringement proceedings and by promoting discussion on the adequacy of investment protection within the single market. Achmea thus arose against a background of pre-existing institutional and legal controversy.

• Facts and Procedural History

The dispute originated in Slovakia’s reform of its health insurance market.

After opening the market in 2004 to national and foreign private sickness insurance operators, Slovakia partly reversed that liberalization and, by a 2007 law, prohibited the distribution of profits generated by private sickness insurance activities. Achmea, a Dutch investor operating in Slovakia through a local subsidiary, claimed that those measures had damaged its investment and in 2008 initiated UNCITRAL arbitration pursuant to Article 8 of the 1992 Netherlands-Slovakia Bilateral Investment Treaty (NL-SK BIT).

Slovakia objected to the tribunal’s jurisdiction, arguing that after its accession to the EU, the arbitration clause had become incompatible with EU law. The arbitral tribunal rejected that objection and, in 2012, awarded damages in favour of Achmea. Slovakia then sought to set aside the award before the German courts at the seat of arbitration in Frankfurt.

After the Higher Regional Court of Frankfurt dismissed the action, the Federal Court of Justice of Germany referred questions to the CJEU on whether Articles 344, 267 and 18 TFEU precluded the application of an arbitration clause contained in an intra-EU BIT.

• The Court’s reasoning

The Court’s reasoning was concise in form but far-reaching in constitutional significance.

It began from the premise that Member States cannot conclude agreements that undermine the autonomy of the EU legal order or alter the allocation of powers laid down by the Treaties. That legal order, in the Court’s view, is characterized by primacy, direct effect, mutual trust, and sincere cooperation. Its autonomy depends on the preservation of a judicial system capable of ensuring the uniform interpretation and application of EU law.

From this starting point, the Court identified three related defects in the arbitration clause contained in Article 8 of the NL-SK BIT. First, the arbitral tribunal could be required to interpret or apply EU law, since the BIT directed it to take account of the law in force in the host State, as well as other relevant agreements between the contracting parties.

Second, the arbitral tribunal was not part of the judicial system of either Member State and could not therefore be regarded as a ‘court or tribunal of a Member State’ for the purposes of Article 267 TFEU. The preliminary reference mechanism, which is central to the uniform interpretation of EU law, was therefore unavailable. Third, the review of arbitral awards by national courts was too limited to ensure that questions of EU law could, where necessary, reach the Court of Justice.

The Court also drew a distinction between treaty-based investor-State arbitration and commercial arbitration. The latter arises from the freely expressed wishes of private parties. By contrast, treaty-based investor-State arbitration derives from an agreement by which Member States remove certain disputes from the jurisdiction of their own courts and, with them, from the system of judicial remedies established by EU law. For those reasons, the Court considered that the arbitration clause endangered the autonomy of EU law and the uniformity of its interpretation.

On that basis, the Court held that Articles 267 and 344 TFEU precluded a clause such as Article 8 of the BIT. Read in those terms, the judgment was not limited to the invalidation of a single arbitration clause, but addressed more broadly the compatibility of treaty-based intra-EU arbitration with the constitutional structure of EU legal order.

• Advocate General Wathelet’s Opinion

Advocate General Wathelet adopted a markedly more permissive view of intra-EU investor-State arbitration than the Court. In his Opinion, he considered that the arbitration clause in the Netherlands-Slovakia BIT was compatible with EU law and did not infringe Articles 18, 267, or 344 TFEU.

On the alleged discrimination contrary to Article 18 TFEU, he argued that the bilateral nature of a BIT necessarily limits its benefits to investors from the contracting States and that this asymmetry is an inherent feature of reciprocal treaties rather than prohibited nationality-based discrimination.On Article 267 TFEU, Wathelet advanced an expansive reading of the concept of a ‘court or tribunal of a Member State’. He considered that the arbitral tribunal established under the BIT operated within a defined legal framework, applied rules of law, and exercised jurisdiction once the investor accepted the standing offer to arbitrate. On that basis, he concluded that such tribunals should in principle be able to make preliminary references to the Court of Justice.

On Article 344 TFEU, he maintained that investor-State disputes under the BIT were neither disputes between Member States nor disputes concerning the interpretation or application of the Treaties in the relevant sense. He further maintained that the arbitral tribunal’s jurisdiction was confined to alleged breaches of the BIT, thus falling outside the scope of Article 344 TFEU. Moreover, in his view, domestic courts retained sufficient control at the annulment and enforcement stages to safeguard compliance with EU law.

The Court did not accept that approach. It refused to regard the arbitral tribunal as part of the judicial system of a Member State and considered the available domestic judicial review insufficient to preserve the autonomy and uniform interpretation of EU law. The disagreement matters because it shows that Achmea was not merely a straightforward application of settled principles, but a judgment that resolved a genuine constitutional conflict over the place of intra-EU investor-State arbitration within the Union legal order.

• The Consequences of Achmea

Implications for intra-EU BITs

Formally, the Court ruled only on Article 8 of the Netherlands-Slovakia BIT.

Substantively, however, its reasoning was framed in structural terms and was widely understood as extending to other similarly drafted intra-EU BIT clauses. That broader significance was reinforced by the intervention of several Member States, aware that the Court’s answer could affect other pending intra-EU arbitrations.

Institutional and practical aftermath

Achmea also had important institutional and practical consequences.

It reinforced the Commission’s long-standing position that intra-EU BITs were incompatible with EU law and accelerated efforts to bring them to an end. Member States subsequently committed to terminate those treaties, a process later reflected in the plurilateral termination agreement.

The post-Achmea response was not limited to treaty termination. It also involved a broader strategy directed at pending arbitrations and the enforcement of awards, with Member States and EU institutions relying on the judgment to challenge the continuation of intra-EU proceedings and to resist recognition or enforcement where such awards were brought before national courts.

The position of extra-EU BITs

Achmea did not directly address agreements involving third countries, and its reasoning cannot simply be transposed without qualification. The constitutional problem identified by the Court was especially acute because the arbitration clause at issue was created by Member States among themselves, thereby establishing, within the Union, a dispute-settlement mechanism capable of affecting EU law while remaining outside the judicial system of the Treaties.

Agreements involving third countries do not raise the same issue in exactly the same form. Even so, questions may still arise where an arbitral tribunal is required to apply the domestic law of a Member State, or otherwise to engage with EU law as part of the applicable legal framework. In that sense, Achmea does not resolve the position of extra-EU BITs, but it does indicate the type of constitutional concern that may arise where the autonomy of EU law is engaged.

Conclusion

Ultimately, the significance of Achmea lies in the constitutional logic of the Court’s reasoning. The judgment did not treat the arbitration clause in the Netherlands-Slovakia BIT as problematic merely because it created an alternative forum for dispute settlement, but because it did so in a manner capable of displacing disputes involving EU law from the judicial system established by the Treaties. In that respect, Achmea significantly reshaped the legal position of intra-EU BIT arbitration by linking it directly to the autonomy and uniform interpretation of the Union legal order.

The contrast with Advocate General Wathelet’s Opinion confirms that the case reflected a genuine constitutional disagreement, not merely a technical divergence over treaty interpretation. Although the Court’s judgment appeared to settle the matter in unequivocal terms, debate over the role of BITs and investor-State arbitration has not been entirely extinguished. It remains possible that future developments may test the boundaries of the Court’s approach, even if they do not displace its central holding.

For now, however, Achmea remains the clearest expression of the principle that dispute-settlement mechanisms engaging EU law must remain compatible with the constitutional structure of the Union.