Taoiseach Leo Varadkar will sack Junior Health Minister Catherine Byrne if she abstains in a vote of no-confidence in Housing Minister Eoghan Murphy.
Speaking as he attended the UN in New York, Mr Varadkar said: "It's, of course, the case that if a Minister can't express confidence in their own colleagues then they can't continue as a Minister."
Ms Byrne is threatening to ignore an order by Mr Varadkar for Fine Gael TDs to rally around the embattled housing minister during a Sinn Fein motion of no confidence tonight.
The row centres over Ms Byrne's concerns that the redevelopment of the St Michael's site in Inchicore is too rent-focused and will ignore local family needs for permanent housing.
The Taoiseach said he will be meeting with Ms Byrne tomorrow when he returns from the US, but said she had not raised the no-confidence vote with him.
He said he can "absolutely understand" the objections that Ms Byrne has to the building of houses in her constituency.
Turning to the Budget, the Taoiseach said he will not be repeating Fianna Fáil mistakes of the past by giving away sweeteners ahead of a General Election.
Mr Varadkar said the upcoming Budget will be "sensible, prudent and modest" and public service pay restoration would be done in a way that is affordable.
He said it "was only right and just" to begin restoring the pay of doctors, teachers, nurses and other public servants.
"You will remember under Fianna Fáil there were massive increases in spending, massive cuts in tax that's not the kind of think we are going to be doing," said Mr Varadkar.