The European Stability Mechanism (ESM) Treaty was signed on July 11 2011. It was later renegotiated and a new ESM Treaty was signed on February 2, 2012. The Treaty provides a permanent emergency fund that is intended to succeed the temporary emergency funds. It entered into force on September 27, 2012 for 16 contracting parties (Estonia completed ratification on October 3). The 17 contracting parties are the member states of the Eurozone, but the ESM Treaty is concluded outside EU law.
(http://www.european-council.europa.eu/eurozone-governance/esm-treaty-signature?lang=it and http://www.esm.europa.eu/pdf/FAQ%20ESM%2008102012.pdf)
What political/legal difficulties did Croatia encounter in the negotiation of the ESM Treaty, in particular in relation to the implications of the treaty for (budgetary) sovereignty, constitutional law, socio-economic fundamental rights, and the budgetary process.
Croatia is not a member of the Eurozone.