LJUBLJANA (Reuters) – Slovenian Prime Minister Miro Cerar has canceled a visit to Croatia planned for Sept. 27 amid a dispute over a border arbitration ruling, Cerar’s cabinet said on Friday.

Croatian Prime Minister Andrej Plenkovic had told the U.N. General Assembly that the June ruling by the Permanent Court of Arbitration determining parts of the countries’ shared sea and land border was not valid.

After Plenkovic’s speech, Cerar told reporters in New York: “The arbitration ruling is valid and internationally binding … as it was reached by five international judges with high authority.”

The Croatian government was not available for immediate comment on Friday.

In its ruling, the court accepted Slovenia’s argument that it should have direct access to the international waters of the Adriatic.

Croatia has said in the past that the border line should be determined in bilateral talks. It withdrew from the arbitration process in 2015 after a leaked tape showed a Slovenian judge on the panel improperly exchanging confidential information with the Ljubljana government.

Slovenia and Croatia both declared independence from the former Yugoslavia in 1991 and have since joined the European Union.

Slovenia has said it will turn to the EU for help if Croatia refuses to implement the ruling. The EU has said that arbitration rulings have to be respected, but is not clear what action it could take.