Malcolm Turnbull is still prime minister for now but Peter Dutton, Scott Morrison and Julie Bishop are preparing to contest any Liberal leadership spill.
Mr Turnbull is forcing Liberals who want him gone to reveal themselves, setting a deadline of midday on Friday for the second leadership challenge of the week.
He demanded Mr Dutton get at least 43 signatures to force a leadership spill – and promised to quit as prime minister if it goes ahead.
That would open the door for Mr Dutton, Mr Morrison and now Ms Bishop to battle it out.
The decision on Thursday afternoon by deputy Liberal leader Bishop – who has successfully bridged the moderate-conservative divide in the party – to canvass support could split off MPs who were considering backing Mr Dutton.
Mr Turnbull has warned Mr Dutton he better be eligible to sit in parliament after questions were raised about his financial interests in childcare centres.
“Australians will be rightly appalled by what they’re witnessing in their nation’s parliament today and in the course of this week,” Mr Turnbull told reporters in Canberra on Thursday.
“The reality is that a minority in the party room, supported by others outside the parliament, have sought to bully, intimidate others into making this change of leadership that they’re seeking.”
The prime minister has lost 13 ministers, including loyalist Mathias Cormann, after they told him the numbers had moved behind Mr Dutton.
“I can’t ignore the fact that a majority of colleagues in the Liberal Party party room are of the view that there should be a change,” Senator Cormann told reporters, adding it came with a “heavy heart”.
Mr Turnbull expects the solicitor-general to provide MPs with advice on whether Mr Dutton is eligible to sit in parliament before Friday’s meeting.
The former home affairs minister has his own legal advice that his interest in childcare centres – which receive funding from the federal government – does not breach section 44 of the constitution.
The section bans from parliament anyone with “any direct or indirect pecuniary interest with the public service of the Commonwealth”.
“This is a very, very significant point,” Mr Turnbull said, having battled through the MP citizenship saga.
“I cannot underline too much how important it is that anyone who seeks to be prime minister of Australia is eligible to be a member of parliament.”