Irish parties are to hold crisis talks after the Greens pulled out of the coalition led by beleaguered Prime Minister Brian Cowen.
The decision by the Green Party wipes out the governing coalition's two-seat majority and puts into question the passage of a vital finance bill.
Mr Cowen quit on Saturday as leader of his Fianna Fail party but is staying on as prime minister.
Opposition parties are threatening to bring down the government.
BBC Ireland correspondent Mark Simpson reports from Dublin that Mr Cowen is clinging onto power, and could well be voted out of office before the end of the week.
On Monday, negotiations will be held between the main parties in Dublin to try to reach an agreement on a timetable for the finance bill and on a date for a general election.
Irish voters are currently due to go to the polls on 11 March.
There is recognition on all sides that the political squabbling is damaging Ireland's reputation abroad, our correspondent says, but a deal is by no means guaranteed.
The opposition has tabled a no-confidence motion for Tuesday.
'Farcical'
Fianna Fail had urged the Greens to stay in government to ensure the finance bill - needed as part of Ireland's international bail-out package - was passed before the election.
It is designed to cut the government's deficit. Ireland was forced to accept the 85bn euro ($113bn; £72bn) EU and IMF bail-out in November last year.
The Green Party will join the opposition benches immediately.
But it said it would still support the finance bill and hoped Fianna Fail would fast-track the legislation so it could be approved speedily.
After the Greens' announcement, Mr Cowen said: "The important thing now is to have an orderly completion of the finance bill in the interests of the country and then obviously we move to a dissolution of the [parliament] and a general election."
Opponents said his decision to stay on was "farcical".
The loss of two Green Party cabinet members means Mr Cowen now only has seven ministers of 15, the minimum constitutionally allowed.
Mr Cowen has been under increasing pressure over his handling of the economy and party disputes.
Last Tuesday, he won a vote of confidence in his leadership of Fianna Fail. Minister for Foreign Affairs Micheal Martin, who had opposed Mr Cowen, resigned.
However on Thursday, Mr Cowen bungled a planned government reshuffle. The Greens were angered and blocked the reshuffle. Mr Cowen then called the general election.
