The Israeli Labour Party has warned that it will bring down the government if Prime Minister Ariel Sharon refuses to meet its new leader immediately.
Amir Peretz took over as Labour leader on Thursday
Amir Peretz wants to pull the party out of the governing coalition and discuss a date for an early election.
Mr Sharon delayed a meeting initially scheduled for Sunday until Thursday.
Mr Peretz said Mr Sharon had acted irresponsibly, as it was better that the Labour Party leave the government in a "co-ordinated way".
"If a meeting with Sharon does not take place at the beginning of the week, we may act to topple the government on Wednesday," Mr Peretz told Israeli television.
"I have political means to act and I will not allow Sharon to behave as though political ground is his private property," he said.
Mr Peretz said he would propose to Mr Sharon holding elections in March or May, advancing a vote not due until November 2006.
All six Labour cabinet ministers in the Sharon government agreed with him on the need to leave the government, he added.
The Moroccan-born trade union leader has accused Mr Sharon of neglecting Israel's poor.
Israel's parliament is expected to vote on several no-confidence motions on Wednesday, and support from the centre-left Labour Party is crucial if the government is to survive.
An election must be held within 90 days if parliament passes a no-confidence vote.
Labour entered government in January as a junior partner in the coalition led by Mr Sharon, the leader of the right-wing Likud party, to support his plans to pull Israeli troops and settlers out of the Gaza Strip.