CANBERRA, Australia (AP) — Australia's beleaguered Prime Minister Tony Abbott will face a second challenge to his position this year, with a ballot of government colleagues late Monday hours after a senior minister challenged him for his party leadership.

Former Liberal Party leader and Communications Minister Malcolm Turnbull asked Abbott to open the party's leadership to an internal vote as the two-year-old conservative coalition government struggles in opinion polls.

The contest will pit a man who has been described as the most socially conservative Australian prime ministers in decades against a challenger some think is not conservative enough.

Unlike Abbott, Turnbull supports gay marriage, wants Australia to replace the British monarch with an Australian president as head of state, and backs a policy of making polluters pay for their carbon gas emissions.

Abbott announced the ballot of ruling Liberal Party lawmakers would be held in Parliament House late Monday.

"This country needs strong and stable government and that means avoiding at all costs Labor's revolving-door prime ministership," Abbott told reporters, referring to the opposition Labor Party that changed its prime minister twice in three years.

"The prime ministership of this country is not a prize or a plaything to be demanded. It should be something which is earned by a vote of the Australian people," he added.

Turnbull earlier said the government was doomed to defeat with Abbott at the helm.

"Ultimately, the prime minister has not been capable of providing the economic leadership our nation needs," Turnbull told reporters. "He has not been capable of providing the economic confidence that business needs."

The government's most senior finance minister, Treasurer Joe Hockey, pledged his support for Abbott, effectively ruling himself out of any future Turnbull cabinet.

"The disloyalty of some has been outrageous," Hockey told reporters, referring to government lawmakers who have undermined Abbott.

"The prime minister has my absolute loyalty, as I have his," Abbott added.

Turnbull might not be the only candidate. Foreign Minister Julie Bishop, the Liberal Party deputy leader, is regarded as a possible contender, as is Social Services Minister Scott Morrison.

Nick Economou, a Monash University political scientist, was not prepared to predict an outcome.

"The Liberals have done enormous damage to themselves, regardless of the outcome," Economou said. "I find it hard to believe that someone would move on the leadership unless they were absolutely confident of their numbers."

The vote continues an extraordinarily volatile period in Australian federal politics, especially as the Liberals were elected in 2013 as a stable alternative to the then Labor government. Labor came to power under Kevin Rudd at elections in 2007, only to dump him for his deputy Julia Gillard in 2010 months ahead of elections. The bitterly divided and chaotic government then dumped Gillard for Rudd just months before the 2013 election.

Before Rudd was elected in 2007, John Howard was in power for almost 12 years.

The government has trailed the opposition in a range of opinion polls since April last year. Abbott survived a leadership challenge from within his party in February that was prompted by those polls and what some say were questionable judgments he made. At the time, Abbott asked his colleagues to give him six months to improve his government's popularity.

That deadline passed without a change in polling. General elections are due around September next year.

Turnbull, a 60-year-old former lawyer and merchant banker known for his moderate views, has long been considered Abbott's chief rival. Turnbull was opposition leader for two years before he lost a party-room ballot by a single vote to Abbott in 2009. His downfall was his belief that Australia should make polluters pay for their greenhouse gas emissions.

Opinion polls show that Turnbull is more popular than Abbott, but many of those who prefer him vote for the center-left Labor Party.

Turnbull is the type of classical liberal that has become rare in the oddly named party, which has been overrun by conservatives in recent decades. It was called the Liberal Party when it was established in the early 1940s because it believed in individual freedoms, while their Labor opponents favored state control and heavy regulation.

Abbott and Turnbull are both Rhode scholars. Abbott, a 57-year-old former Roman Catholic seminarian, has long suffered an image problem, particularly among women. He is regarded as gaffe-prone and old-fashioned in his views on women's place in society.

Turnbull is a self-made multimillionaire regarded by some as arrogant and has been nicknamed "The Silvertail," an Australian term for wealth and privilege.