The oral hearing is planned under Article 259 of the Lisbon Treaty under which an EU member state can take a fellow member country to the EU Court of Justice for violating the EU's law.
The article was invoked by Slovenia in mid-March over violations related to Croatia's failure to implement the shared border as set by an arbitral tribunal on 29 June 2017.
Unofficial information indicates that the oral hearing will be attended by delegations of experts from Slovenia, Croatia and the European Commission.
The Commission is to be represented by the Legal Service and Slovenia by Foreign Ministry officials. The hearing will be conducted behind closed doors in Slovenian, Croatian and English.
The hearing is scheduled to start at 2:30 PM. After introductory notes from the Commission, each side would have half an hour to present their position and another ten minutes each to respond to the other's positions.
The Commission would then have half an hour for its questions or response, followed by five minutes for each party's closing arguments and another ten minutes for the Commission's conclusions. The hearing is to conclude at 4:50 PM.
Slovenia and Croatia are expected to present their well-known positions. The Commission is not expected to introduce any political initiatives at this expert level and unofficial information indicates that the Commission has not made any proposal so far, either officially or unofficially.
In announcing the date of the oral hearing earlier this month, the Commission called on Croatia to respond in writing to Slovenia's letter setting out its case.
Croatia's response, which unofficially runs to some 15 pages without the attached documents, was later referred by the Commission to Slovenia.
Unofficially, the Croatian response does not contain any surprises. The gist of it is said to be Croatia's well-known position that the country does not violate the EU's law so the EU does not have a jurisdiction over the issue.
The position is not quite in agreement with past comments by Croatian Prime Minister Andrej Plenković; on the sidelines of the EU summit in Brussels on 22 June, he asserted that for Croatia arbitration was a bilateral issue and an international law issue that might in smaller aspects be related to the acquis, for instance in the case of fisheries.
The content of the Slovenian letter remains confidential, but the information so far suggests it contains instances of concrete violations due Croatia's rejection of the border arbitration award.
These include contraventions of principles of the rule of law, preventing Slovenia from implementing the EU's law and violations of Schengen rules and common fisheries rules.
The Commission would like a political solution "within the family", having noted in announcing the oral hearing that it was important to stick to "the letter and spirit of Article 259", which provides an opportunity to "address legal conflicts within the family".
The Commission also underscored that the oral hearing was the first procedural step that all other steps would depend on.
The question is what the Commission will do and it remains to be seen whether its reaction is to be expected right after the hearing or later.
Article 259 gives the Commission three months to take a position, but it may also not do so. Even if it does not take a position, unofficial expectation is that the Commission will notify both sides of that.
The Commission has been creating the impression that it does not get involved in the Slovenian-Croatian dispute and the signals this far does not indicate it will. A while ago Commission President Jean-Claude Juncker went as far as stating that this was an "issue nobody is taking interest in".
The Commission's Legal Service has confirmed a connection between the arbitration award and the EU's law. As soon as the arbitration award was announced, the Commission urged both countries to implement it. The Commission has also been offering its mediation, but without any concrete steps so far.
Despite Croatia's refusal to implement the award, the Commission, whose leadership comes from the same European political group as Plenković, has done nothing.
President of the European Court of Justice Koen Lenaerts has recently suggested that Slovenia could try resolving the matter by applying Article 273 of the Lisbon Treaty, under which member states submit their dispute to the court by agreement in cases that are not strictly EU law but are important in a broader sense.
Unofficially, Slovenia deems the option unfeasible because Croatia is not expected to agree to such a step, considering that taking the dispute to court does not appear to be in Croatia's interest.
