Italian Prime Minister Romano Prodi is set to address parliament after the departure of an ally threatened to topple his fragile ruling coalition.
Mr Prodi came to power as the winner of the April 2006 election
Speaker Fausto Bertinotti said the centre-left PM had asked to address the lower house, the Chamber of Deputies, on the "general political situation".
There had been speculation he would resign on Monday after a former ally ruled out rejoining the government.
Clemente Mastella, the former justice minister, called for an early election.
His centrist Udeur party has three seats in the upper house and its withdrawal has cost Mr Prodi his Senate majority of one.
Mr Mastella, who quit last week after being implicated in an ongoing corruption inquiry, told reporters Mr Prodi's coalition was "finished".
He said he would oppose the government in any vote of confidence.
The BBC's Christian Fraser reports from Rome that is still possible for Mr Prodi to govern with the support of several unelected life senators but the question is: for how long?
Mr Mastella had promised last week to continue supporting Mr Prodi on a case-by-case basis.
ITALIAN ELECTION RESULTS
Composition of parliament immediately after April 2006 election
But the ex-minister, who at times has been accused of holding the government to ransom, said the experiment with the centre-left was now over.
"We are for elections and if there is a confidence vote in the future we will vote against the government," he said.
On Wednesday, Environment Minister Alfonso Pecoraro Scanio faces a vote of no confidence in the Senate for his handling of the rubbish crisis in Naples.
Defeat for him would undermine Mr Prodi's position despite the majority his coalition enjoys in the Chamber of Deputies.
Antonello Soro, the parliamentary chief of Mr Prodi's Democratic Party, has said the coalition is unravelling at the seams.
"I cannot exclude the possibility that at the end of it all we'll be obliged to go to the polls," he said as the coalition held crisis talks.