This is about the rule of law and there is no other option, Mayer said, quoting EU Justice Commissioner Viviane Reding as saying in Brussels on Tuesday that it was completely unacceptable that the amendments to the Croatian law on EAW application should take effect as late as mid-2014 and that Croatia should immediately implement the law in the form in which it had signed it. He stressed that Reding had the support of the entire Commission.

If Zagreb changes its position in the next 10 days, there should be no long-term political consequences for Croatia despite this breach of trust, Mayer said.

The European Commission on Wednesday began consultations with the member states to activate a safeguard clause provided for in the Croatian accession treaty because just days before its entry into the EU Croatia had passed a law limiting the application of the EAW to crimes committed after August 2002, which the Commission said was in violation of the accession treaty.

In a document addressed to the member states, the Commission says that Croatia had correctly transposed the European Arrest Warrant through the Act on Judicial Cooperation with EU Member States in 2010 and based on that the EU accession negotiations were concluded and the accession treaty ratified by the national parliaments of the 27 member states. "On 28 June 2013, the Croatian parliament adopted far-reaching changes to its national law implementing the European Arrest Warrant. This was done despite warnings from the Commission that such amendments were incompatible with EU law," Commission President Jose Manuel Barroso, Vice-President Viviane Reding and Enlargement Commissioner Stefan Fuele said in the document.