Slovenia's outgoing government filed a case Friday against neighbour Croatia at the EU's General Court, accusing it of breaching EU law by refusing to implement an arbitration ruling on a border dispute.
"The government decided to file the suit immediately," an official statement said, accusing Croatia of not implementing a June 2017 ruling from the Permanent Court of Arbitration in The Hague, which allocated Slovenia more than two-thirds of the picturesque Piran Bay.
Zagreb has refused to recognise the decision and has urged Slovenia to instead start fresh negotiations on the border spat, which has raged since both countries declared independence from the then Yugoslavia in 1991.
The EU-backed arbitration court had given both parties six months to implement its decision, but after the deadline expired in December, police patrols from both countries started fining each other's fishermen for border and fishing violations.
Before filing the complaint, Slovenia had asked the European Commission to put pressure on Croatia to implement the ruling, or to launch formal procedures against it.
But last month Brussels urged both sides to seek a solution amongst themselves and offered its mediation if necessary.
Cars queue in line at the Croatian border with Slovenia in Bregana, near Zagreb on April 14, 2017