Maverick MP George Christensen is threatening to cause chaos in parliament unless the government acts quickly to protect Australians from “vaccine discrimination”.
The Coalition controls 76 of 151 members of the House of Representatives, including the Speaker.
If Mr Christensen was to follow through on his threat and cross the floor, the government would need the support of Labor or a crossbencher to pass legislation.
The Queenslander’s rebellion means the government will have a hard time getting its religious discrimination bill, voter identification reforms, and a federal anti-corruption commission through the lower house.
Mr Christensen’s threat comes a day after One Nation leader Pauline Hanson tried unsuccessfully to pass a bill in the Senate, which sought to ban mandatory vaccinations and overturn state and territory leader’s requirements for full vaccination to be required in some settings.
Liberal backbenchers Gerard Rennick and Alex Antic crossed the floor to vote alongside Senator Hanson and fellow One Nation senator Malcolm Roberts.
Coalition senators Matt Canavan, Sam McMahon and Concetta Fierravanti-Wells also voted for the bill.
In response, senator Jacqui Lambie gave an impassioned plea for unvaccinated Australians to be a “Goddamn bloody adult” and put others before themselves.
Senator Rennick and Senator Antic have pledged tto withhold support for all government legislation until state-based vaccine mandates are overturned.

Late on Monday, Mr Christensen shared a blog post throwing his support behind Senator Hanson, Senator Rennick and Senator Antic.
He vowed to spend the final seven sitting days of this year causing havoc for the government unless it agrees to his vaccine mandate demands.
“Earlier today, I informed Nationals leader Barnaby Joyce (and the Nationals party room of which I am a member) that, unless we act to stop state governments and private corporations from discriminating against non-vaccinated Australians when it comes to either employment or clientele, then I intend to not be beholden to party room discipline when voting in the House of Representatives,” he said.
“To be clear, until federal action is taken against vaccine discrimination, I will be voting according to my conscience (or abstaining from votes) on bills and substantive motions rather than just voting with the government as MPs usually do.”
Mr Christensen said as a member of the LNP, he would continue to support the government with confidence motions and supply as well as procedural motions – except if they relate to ending vaccine discrimination.
“My support is not guaranteed,” he said.
“When action is taken to stop vaccine discrimination, I will go back to the normal process of voting with the government on most, if not all, bills and substantive motions.”

Prime Minister Scott Morrison said on Monday, after the Liberal senators crossed the floor, that the coalition “ (doesn’t) run as an autocracy”.
“We don’t kick people out of our party if they happen from time to time to disagree on issues on which they feel strongly,” he said.
“We don’t agree with the measures that were in (Senator Hanson’s) bill … but I respect the fact that individual members from time to time will express a view and they’ll vote accordingly.”
Mr Morrison has voiced his criticism of state and territory mandatory vaccination laws, but will not support legislation that would effectively overturn them.
Mr Christensen said he anticipated his stance would result in personal attacks, but he would not back down.
“Far more important than my political and personal reputation is the prospect of ending the tyranny, the discrimination, the segregation, the job losses, and the negative business impacts that are being wrought on my fellow Australians,” he said.
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