Addressing the press, Milanovic said that the Opposition coalition "is for changes and we are not interested in what Prime Minister (Jadranka Kosor) will say" at a convention which the ruling Croatian Democratic Union (HDZ) is due to hold later in the day.
"We are not interested in what they will say, it is the the HDZ's business," Milanovic said.
Pusic added that the HDZ had already shown what they could do.
Asked by reporters whether he was sorry that he would not sign Croatia's accession treaty with the EU, Milanovic said that there was no room for envy.
"As far as we are concerned, it would be better if the treaty had already been signed. It is irrelevant who will sign it now that the matter is finished," the SDP leader said, adding that his message to Kosor would be to look what she would sign.
Milanovic accused the government of selling a stake in the Janaf oil pipeline operator for the compensation of pension recipients for non-indexation of pensions in the past.
He said that the state's interest in Janaf would thus fall below 75 per cent which he considered to be dangerous for Croatia's energy independence, describing Janaf as a strategically important state company.
The SDP leader went on to say that the debt to pensioners should be paid back as proposed by the Constitutional Court.
Leaders of the Croatian Pensioners' Party (HSU) and of the Istrian Democratic Party (IDS), the other two parties in the centre-left opposition coalition, today presented the 21-point plan in Pula.