Taoiseach Leo Varadkar has said he will sack Minister of State Catherine Byrne if she does not support Housing Minister Eoghan Murphy in tonight's motion of no confidence.
Ms Byrne has told ministerial colleagues she is considering supporting or abstaining on a Sinn Fein motion of no confidence in Mr Murphy.
Ms Byrne has been at war with Mr Murphy over the development of 470 new homes in her constituency.
During the summer, she took to the stage at the launch of the project to say it was the "worst plan" she had ever seen.
Since the intervention, she has continued campaigning against the State's first not-for-profit rental accommodation on the St Michael's House site in Inchicore, Dublin.
Ms Byrne believes the cost rental model is not appropriate for her area as it will not benefit local families.
Her relationship with Mr Murphy has been extremely strained since her public criticism of his plan.
However, speaking after a United Nations meeting in New York yesterday, Mr Varadkar said he would be forced to sack Ms Byrne if she does not support her Government colleague in the Dail tonight.
"It is of course the case if a minister can't express confidence in their own colleagues then they can't continue as a minister," Mr Varadkar said.
The Taoiseach said Ms Byrne had not directly raised the motion with him but had spoken to him about her objections to the Inchicore development.
"She has come to me with her objections to the building of 500 new homes in her constituency and I have heard what she had to say about that, but we are in a housing crisis and we do need to build new homes and particularly at higher densities. We need a mix of housing as well because everyone deserves a home," he said.
He said he does not have the authority to block housing projects but even if he did he would not stop the development.
Several high-level Government sources yesterday confirmed Ms Byrne had privately threatened to support or abstain from the no-confidence motion tabled against Mr Murphy by Sinn Fein.
Several sources said Ms Byrne had told ministerial colleagues that she was prepared to take the extraordinary action in response to Mr Murphy's failure to listen to her concerns about the St Michael's House project.
It is understood she told ministers she would not back her Fine Gael colleague unless plans for the site were dramatically changed.
She told them she believed Mr Murphy did not understand the impact of the development on her local community.
"This is potentially very serious but there is a while to go before the vote on the motion [tonight]," one Government source said.
"She could have just not turned up in the chamber but she's told so many people now it would have been obvious that she wasn't backing Eoghan."
The move would present the Government with serious difficulties ahead of the debate on Mr Murphy's handling of the housing crisis.
The Government's small majority means that Ms Byrne's vote is essential to ensure Mr Murphy remains in his ministerial portfolio.
Fianna Fail has decided to abstain on the vote but Dail arithmetic means the Taoiseach will need every Government TD in the chamber to ensure the motion is defeated.
Mr Varadkar has already told TDs and ministers to cancel their travel plans ahead of the crucial Dail vote.
The St Michael's House project would consist of 470 new homes, with 30pc reserved for social housing, 60pc rented to low and middle-income earners and the remaining 10pc assigned for affordable housing.
Ms Byrne recently wrote to Dublin city councillors saying anti-social behaviour and crime in her constituency should be addressed before the site is developed.
"I believe that the proposal on the table for the former St Michael's estate site is simply the wrong one if it doesn't include an option for long-term permanent housing alongside amenities and services which would benefit the community as a whole," she said.
Ms Byrne did not respond to requests for comment.