The hearing will likely be held behind closed doors, as stipulated in the arbitration treaty signed by the countries in 2009. A decision from the arbitration tribunal is expected in the first half of 2015.

Slovenia recently proposed that the hearing be public, but Croatia objected the idea. Slovenia's representative at the court, Simona Drenik, told the press in Ljubljana today that Slovenia did not demand a public hearing but only proposed this.

Unless Croatia agrees with the proposal, the hearing will be held behind closed doors, she said and rejected allegations by Croatia that Slovenia requested a public hearing to delay the procedures.

Drenik talked to the press after Slovenia submitted to the tribunal its response to Croatia's counter-memorandums. She said that the 200-pages document addressed issues and contentious facts stated by Croatia in its counter-memorandum. Slovenia's response also includes 180 pages of additional documents.

So far, the countries presented their cases in written memorandums sent to the tribunal in February 2013. Then they responded to each other's cases with counter-memorandums in November. This was also the last step defined in the arbitration treaty before the hearing.

However, the tribunal approved Slovenia's request for one more round of written explanations under the rules of the Permanent Arbitration Court, as the country found that some of Croatia's statements in the counter-memorandum were incomplete and misleading, said Drenik.

After the oral hearing, the tribunal will withdraw for deliberation and a decision is expected for the first half of 2015. The five member tribunal will be deciding on the course of the border in several contentious sections on land and sea.

The official cases of the two countries have remained a secret. It is however clear from the countries' past efforts that Slovenia will demand to preserve the integrity of the Piran Bay and have access to international waters, while Croatia wants the sea border to run directly in the middle of the bay and to leave Slovenia without a corridor to the high seas.