The Turnbull government could face increased pressure from crossbench senators on a range of issues after being accused of breaking a deal with key supporter David Leyonhjelm.
The Liberal Democrats senator wants Malcolm Turnbull to honour his agreement to guarantee a vote in both houses on legislation to lift the ban on territories legislation on voluntary euthanasia.
Senator Leyonhjelm said it was a matter of honour for the prime minister.
He pointed to the implications that reneging on the agreement could have for "future trust and co-operation" between the crossbench and government.
Mr Turnbull argues the deal was only for a vote in the Senate, not both houses.
But Senator Leyonhjelm says the prime minister gave him his word in face-to-face discussions.
The deal was for his crucial support on re-establishing the Australian Building and Construction Commission.
"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."
Souring relations with the crossbench could get messy for the government.
The coalition needs eight of the 10 independent, One Nation and Centre Alliance senators to pass its legislation.
The upper house is set to debate Senator Leyonhjelm's legislation on Tuesday lifting the ban on NT and ACT controlling their own euthanasia laws.
After it is dealt with, corporate tax cuts will be on the agenda, with the government still trying to garner crossbench support for the policy.