Under Article 259, a member state can take another member to the EU's Court of Justice due to violations of EU law.
Slovenia believes that by refusing to implement the border arbitration award announced on 29 June 2017, Croatia violates the principle of the rule of law, undermines Slovenia's ability to implement EU law and violates Schengen rules and common fisheries rules.
Croatia claims it had withdrawn from the arbitration process after it was "irreversibly contaminated" in 2015, when a wiretapping scandal revealed prohibited contacts between the arbitrator appointed by Slovenia and the country's agent.
But the tribunal decided in 2016 that the violation had not been so severe as to derail the process.
Croatia now wants a bilateral agreement, while Slovenia insists that the EU-sponsored arbitration decision must be honoured.
The outgoing government of Miro Cerar decided on 21 June to notify the new Foreign Policy Committee of the lawsuit before filing it at the EU's Court of Justice in Luxembourg. The committee backed on 7 July the government's plan to lodge the suit since nothing has changed about the implementation of the award.
Cerar's government was given already in March parliament's green light to carry through with the suit if the European Commission does not take on the case and if Slovenia does not yet have a new government with full powers after the June election.
Finance Minister Mateja Vraničar Erman said that the government had "decided on filing the lawsuit a while ago, conducted the appropriate debate in the National Assembly, and finished the process without any opposing opinions today."
Slovenia will take Croatia to court on its own, as the Commission did not issue an opinion on the country's plan to sue Croatia by the mid-June deadline.
The EU's Court of Justice will go into recess on Monday, meaning that no activity related to the case is expected before the end of the summer recess, 31 August.
The government said the suit was not public but its assertions would be published by the court in the EU's Official Journal.