Slovenia has submitted a letter proposing a lawsuit against Croatia to the European Commission. The letter is the first step in Slovenia's plan to take Croatia to the EU's Court of Justice over Zagreb’s failure to implement a 2017 border arbitration ruling. 

Croatia refuses to accept the July 2017 Permanent Court of Arbitration (PCA) ruling giving Slovenia access to the high seas through Piran Bay, claiming the process was corrupted. Zagreb’s stance is that it will not accept the ruling after a Slovenian official was discovered trying to influence the outcome back in 2015.

The letter was handed by Slovenia's Ambassador to the EU Janez Lenarcic to Clara Martinez Alberola, the new head of the Commission president's cabinet, Slovenian Press Agency (STA) reported sourcing Slovenia's mission to the EU. This was confirmed by EC spokesman Alexander Winterstein later on March 16.

The letter's content remains confidential, but the information disclosed so far suggests it lists concrete instances of how EU law has been violated because of Croatia's refusal to implement the border between the two countries, according to STA.

Slovenian Prime Minister Miro Cerar said in February that Ljubljana was planning to start proceedings by sending a letter to the European Commission in which it would explain that Croatia had failed to respect Article 259 of the Lisbon Treaty. 

Article 259 of the Lisbon Treaty states that: “A member state which considers that another member state has failed to fulfil an obligation under the Treaties may bring the matter before the Court of Justice of the European Union. Before a member state brings an action against another member state for an alleged infringement of an obligation under the Treaties, it shall bring the matter before the Commission.”

The Croatian government responded angrily to the news, with the foreign ministry saying that Slovenia has “no right or reason” for initiating a case against Croatia, news agency HINA reported on March 16.

The EC now has three months to respond to the letter and to decide whether it will trigger procedure against Croatia before the EU court. If not, Slovenia will resume the procedure itself, STA reported.

The EC said the Commission stands ready to mediate as it did in earlier legal disputes between member states, for example last year in the Almaraz case between Spain and Portugal.