Information on the formal notice was published yesterday in an official Commission register of proceedings for establishing violation of EU legislation.

The file in the register notes that the case relates to the seizure of documents owned by the European Central Bank from the Banka Slovenije premises, which may constitute a violation of EU privileges and immunity rules and statutes related to the European Central Bank.

Slovenia now has two months to respond to the notice. In Thursday's statement, the Commission said it was encouraging the Slovenian authorities to engage in constructive dialogue with the ECB as a means of finding common ground for ensuring that the investigation confirms to EU laws.

Formal notice may be followed by a second warning, called a reasoned opinion, whereupon the country has two months to act to rectify the situation before it is taken to the Court of Justice by the Commission.

The announcement comes after media reported in February that the commission had launched legal proceedings against Slovenia over the July 2016 raid at the Slovenian central bank. The ECB had claimed its data were illegally seized as part of the investigation.

At the time, the Commission denied the reports and said they were in contact with Slovenia and the ECB on the issue. Unofficially, however, the country had been sent a "pilot letter" asking for clarification.

Crime investigators seized extensive documentation at Banka Slovenije in July 2016 as part of investigation into suspected abuse by top central bank officials during the late-2013 bailout.

House searches were also conducted at NLB, Slovenia's largest bank, and two auditing firms on suspicion that NLB unlawfully gained EUR 257m after its liabilities related to subordinated bonds were extinguished due to decisions taken by central bank officials during the bank bailout.

The raids prompted ECB President Mario Draghi to protest with European Commission President Jean-Claude Juncker and Slovenian State Prosecutor General Zvonko Fišer due to the "unlawful seizure" of the ECB's information.

In January the Ljubljana District Court cleared police and prosecution procedures in the raid, after finding that the documents seized did not represent the ECB's archives.

Challenging that ruling, the ECB turned to the Slovenian Constitutional Court last month. The ECB maintains that the documents seized are protected under a special protocol on privileges and immunity under which ECB archives are off-limits to national judicial authorities.