Prime Minister Tony Abbott will face the judgement of his partyroom on Tuesday, with a leadership spill throwing Canberra into weekend chaos.

Bureaucrats will be nervously watching developments, as so-far-undeclared leadership aspirants court support over the coming days. A new prime minister is likely to chart a different course for the government, with major policy shifts possible under likely candidate Malcolm Turnbull and potentially others.

West Australian MPs moved to bring on a spill of leadership positions this afternoon, with Luke Simpkins emailing colleagues to inform them he would be moving for a spill at Tuesday’s first partyroom meeting of 2015. Fellow WA MP Don Randall will second the motion. Earlier in the week another WA MP, Dennis Jensen, was the first to publicly withdraw support for Abbott as party leader.

Just before 2pm today, government chief whip Philip Ruddock issued a statement:

“I have received notice of motion from Luke Simpkins seconded by Don Randall proposing; “‘That the Liberal Party Room resolve, via secret ballot, that the senior positions of the Federal Parliamentary Liberal Party be declared vacant’. “The Prime Minister has indicated this motion will be listed for discussion at the Liberal Party Meeting on Tuesday.”

Under Liberal Party rules, there has to be a majority of support within the partyroom for a leadership ballot to take place, although the incumbent can declare a spill at any time. There are currently 102 Liberal MPs, meaning 52 MPs must support the Simpkins/Randall motion.

But even a smaller level of support would be deeply wounding for an already crippled leader. The worst outcome for the Liberals and the government would be for a substantial number of MPs to back a spill without a result.

There are no challengers currently, with the two frontrunners to replace Abbott — Turnbull and Julie Bishop — having supported the Prime Minister all week. In the last 24 hours, momentum appears to have shifted to Turnbull over Bishop, with a focus on how Turnbull can shore up the support of the Right of the party and the Nationals. The push from WA MPs, however, may indicate he may yet face off against Bishop (like Turnbull, a moderate) backed by conservative forces from the West.

Turnbull lost the Liberal leadership in 2009 at the hands of right-wing forces over the issue of supporting an emissions trading scheme, with considerable agitation from Nationals climate denialists like Barnaby Joyce. In the 2009 contest, Abbott faced off against Hockey and Turnbull, and defeated Turnbull in a second round ballot by one vote. Ironically, Simpkins, Randall and Jensen are all themselves climate denialists.

Abbott dismantled the Department of Climate Change along with throwing out the carbon tax. Turnbull remains supportive of the concept of an emissions trading scheme, but Nationals are understood to be seeking assurances he won’t again advocate for a price on carbon as leader.

Additional reporting from Bernard Keane

The Mandarin sister site Crikey is running a live blog with breaking developments on the spill until Tuesday’s vote …