Julia Gillard, the Australian prime minister, has called for a snap party vote in a bid to end uncertainty over her job.
"I do think it's in the best interests of the nation and in the best interests of the Labor Party for this matter to be resolved," Gillard said, in calling the leadership vote for 7:00pm (09:00 GMT) on Wednesday.
Kevin Rudd, himself a former prime minister and Gillard's intra-party rival, announced that he would challenge the PM for the leadership of the party.
"I will be a candidate," he said at a press conference shortly after the ballot was announced.
Australia's first female prime minister said she would quit politics if she lost the leadership to Rudd, whom she toppled in a leadership coup in June 2010.
Gillard now rules with a one-seat parliamentary majority, with support from the Greens and key independents.
The Greens and key independents have said Rudd, if elected, would need to test his support in parliament.
Opinion polls suggest Gillard will face a defeat in general elections slated for September.