They said that their move was prompted by the behaviour of the ruling Croatian Democratic Union (HDZ) and the damage it was doing to the dignity and reputation of Parliament.

The decision followed a heated debate at a meeting of the parliamentary Credentials and Privileges Commission on Wednesday when Vladimir Seks, a senior HDZ official and deputy speaker of Parliament, made sexist remarks about SDP MP Gordana Sobol, and HDZ MP Tomislav Culjak threw sheets of paper at an SDP member of the Commission in a bout of anger.

"In a situation when communication in Parliament has been reduced to throwing bottles and sheets of paper, as if we were in some dive bar, we can no longer participate in the work of Parliament," said the chair of the HNS/HSU group, Vesna Pusic.

Slavko Linic of the SDP said that the opposition did not want to be "just a decoration in Parliament that doesn't care about the situation in the country". He said that the present Parliament should be dissolved and that it should be left to voters to decide who would represent them in the next Parliament.

When asked what would happen if, because of the absence of the opposition MPs, there was no quorum for making decisions, including one on the interim budget in the first three months of next year, Linic said that it was up to the President of the Republic to act in accordance with his powers if Parliament was not functioning.

HSU leader Silvano Hrelja said that the MPs from their coalition would continue coming to Parliament but would not participate in its work.

IDS deputies did not attend the press conference, but Linic said that the chairman of the IDS parliamentary group, Damir Kajin, fully supported the boycott.

The Croatian Labour Party, which is not a member of the opposition coalition, joined in the boycott. It announced its decision in a written statement, citing "the unprecedented outburst of Deputy Speaker Vladimir Seks and total disregard for the rules of etiquette in Parliament."