Embattled Australian Prime Minister Julia Gillard called a Labour leadership ballot for Wednesday evening amid party-room moves to depose her in favour of predecessor Kevin Rudd.
Gillard said the ballot would be held at 7pm (9am GMT) and said the loser should quit Parliament.
"There are no more opportunities. Tonight is the night and this is it," she told Sky News.
"These issues need to be resolved. Anyone who believes that they should be the Labour leader should put themselves forward."
Asked if she would quit politics if she lost, Gillard said: "Correct."
But she added: "I wouldn't be putting myself forward unless I had a degree of confidence."
Her decision followed widespread reports that a petition was circulating among Labour lawmakers on Wednesday calling for a caucus meeting where a vote on the leadership would be held, amid mounting unease in the party over an expected rout under Gillard at the national elections on September 14.
Gillard said she hadn't seen a petition or been approached about a ballot but "in these circumstances I do think it's in the best interests of the nation and in the best interests of the Labour party for this matter to be resolved".
Parliament is due to rise on Thursday night for the last time before the national polls, so any ballot had to be held before the legislative body disbands.
It brings to a head weeks of speculation about a new challenge by former leader Rudd against Gillard, who is staring at a crushing election defeat by the Tony Abbott-led conservatives, according to opinion polls.
Gillard ruthlessly dispatched Rudd in a 2010 party room coup but he remains popular with the public and is seen by many as Labour's best hope, although he has yet to indicate whether he will stand against her in the ballot.