Senator David Leyonhjelm is weighing up how to retaliate after accusing Malcolm Turnbull of breaking a deal on a bill to restore territories' power to legalise voluntary euthanasia.
On Tuesday the Senate is set to debate legislation lifting the ban on NT and ACT controlling their own euthanasia laws.
The Liberal Democrats senator is adamant the prime minister promised to let his private member's bill be debated in the lower house if it succeeded in the upper house.
However, Mr Turnbull insists no such deal was made.
He says the crossbench senator only asked the government to allow a vote on whether the issue could be debated in the Senate.
"We did not do that. The vote to bring it onto the notice paper was carried despite opposition from government members," Mr Turnbull told ABC radio.
Senator Leyonhjelm says he took the prime minister's word when he agreed to back re-establishing the construction industry watchdog in exchange for a debate and vote on his bill.
"It is very disappointing, but the issue is a long way from over," Senator Leyonhjelm told AAP.
The government needs eight of 10 crossbench senators to get its legislation through the upper house.
Senator Leyonhjelm said crossbenchers had to be assured the government would uphold its side of the bargain.
"Knowing that it hasn't stuck to its deal in this instance would be somewhat significant to many of the crossbench," Senator Leyonhjelm told AAP.
"That will affect the government's relationships in the Senate."
Senator Leyonhjelm said he'd raised the personal guarantee with Mr Turnbull on multiple occasions only to be told it was a matter of timing.
"That was a reference to the fact he has a fairly fractious party room," Senator Leyonhjelm said.
There are fears within the coalition euthanasia debate could cause divisions similar to same-sex marriage last year.
The prime minister confirmed his upper house colleagues will have a conscience vote on the bill, but says he'll have to consider if lower house MPs will be given the same freedom.
"If the vote came on, if I was a senator, I would be voting against it," Mr Turnbull said.
Senator Leyonhjelm is confident he has at least 40 of the required 39 votes to pass the bill in the Senate.
It is understood Indigenous Affairs Minister Nigel Scullion and Labor senator Kristina Keneally are among a group of senators set to support it because they see it as an issue of territory rights.
The NT was the first jurisdiction to legalise voluntary euthanasia in 1995.
But the federal government overruled the territories' rights with its own laws in 1997.
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