Der Spiegel: Most Slovenian claims vs Croatia proven

The German weekly magazine released the eight-page legal opinion, dated 14 May, 2018, which the Legal Service drew up for the Commission before the three-month period expired for a response to Slovenia's proposal under Article 259 of the Treaty on European Union (TEU).

In the document, the Legal Service proposed that the Commission adopt the "reasoned opinion" and to take over the case against Croatia in accordance with the mentioned article. The letter was addressed to the head of the cabinet of the European Commission, and signed by Karen Banks.

Summing up the Slovenia-Croatia border arbitration dispute, the Legal Service's opinion says that Slovenia's complaint is, in essence, that Croatia, by refusing to recognise the arbitration award, prevents Slovenia from fulfilling its obligations and enjoying its rights under EU law.

The Legal Service also noted that the arbitration tribunal in 2016 rejected Croatia's claims that the arbitration process was compromised and that the arbitration agreement was no longer valid.

Thus the only relevant question for the EU is whether it should respect the decision of the international arbitration tribunal and take it into consideration in the application and interpretations of questions of EU law.

The Legal Service notes that the obligation to respect international law must include respect for legal principles such as "pacta sunt servanda" (agreements must be kept) and "res judicata" (respecting a matter already judged), that is including treaties such as the arbitration agreement and the arbitration award.

"In this respect the fact that implementing measures may still have to be taken, as argued by Croatia, cannot mean that it would be possible to disregard the final award and the provisions of the Arbitration Agreement.

"The possible implementation would therefore only concern arrangements on the material demarcation of the border where this is needed (mainly on land) and the adjustment of internal legislation and regulation. In the marine areas the lines have been precisely determined by the award and this aspect would normally not even require any further arrangements on demarcation.

"In the light of the above, and without making any judgements of its own, the Commission must just observe that there is an arbitration agreement which has not been validly terminated and that there has been final determination of the borders between Slovenia and Croatia.

"Therefore the outcome of the arbitration procedure must be respected by the EU, and provisions of EU law must be interpreted in the light of it," the Legal Service's opinion reads.

The opinion also sums up and endorses Slovenia's claims of Croatia's infringements of the general duty of loyal cooperation under Article 4 of TEU, specific duties under the Common Fisheries Policy, specific duties under the Schengen Code and specific duties under Maritime Special Planning Directive.

According to Der Spiegel, the European commissioners responsible for the issue have yet to see the legal opinion. The weekly says that Commission President Jean-Claude Juncker is ignoring his own legal staff's advice, wondering whether this is to help Croatian PM Andrej Plenković, who is a member of the same political party.

The magazine notes that Juncker himself argued that the border dispute between Slovenia and Croatia "must be resolved" when he raised the matter in the European Parliament in February. After all, he said, it is not just a problem for the two EU members, but "a European problem".

"In a strange twist ... it's now the European Commission chief himself who is delaying a solution. The Commission had several opportunities to act as an arbitrator in the conflict, but Juncker decided to stay out of it, even though his own staff has no doubt that Slovenia's position is largely correct in the matter," writes Der Spiegel's Brussels correspondent Peter Müller.

Asked for comment, the Slovenian Foreign Ministry told the STA that it was not commenting on media reports, but that "Slovenia is committed to respecting the rule of law and decisions of international courts. We believe the European Commission shares our view."

Dominika Švarc Pipan, an international law expert who has recently been appointed one of two state secretaries at the Ministry of Justice, tweeted: "No wonder the Commission wouldn't make the opinion public or send it to Slovenia. It'll now be really hard to justify silence or pretend ignorance any longer."

The European Commission would not comment on Der Spiegel's report. In response to a query by the STA, the Commission said it was not commenting on the many internal documents that may be circulating in the Commission.