Government sources have confirmed that Junior Health Minister Catherine Byrne is considering abstaining or even voting against Housing Minister Eoghan Murphy in a motion of no confidence.
The row is over a local housing issue in Dublin and has come to a head after the two previously fell out.
Such a move by Ms Byrne would be in direct defiance to an order by Taoiseach Leo Varadkar to support Mr Murphy in a Dail motion this week. Any such move could see the Dublin South Central TD face party sanctions or possibly even losing the whip.
The disagreement now threatens to engulf the Fine Gael party who are preparing to fight off a Sinn Fein vote and debate of no confidence in Mr Murphy tomorrow night in the Dail.
Government sources this afternoon have confirmed reports to the Irish Examiner that Ms Byrne has let party and government colleagues know her position.
The disagreement is over housing for the St Michael's site in Inchicore, Dublin.
Ms Byrne is opposed to government plans for rental accommodation on the site, claiming this will not benefit local families who want to live in the area.
Both Ms Byrne and Mr Murphy fell out over the issue during the summer, when the junior minister on a stage argued that the plans for St Michael's were the “worst ever” she had seen.
Sources are stressing that the Junior Health Minister has not threatened to vote no or indeed sought specific demands in exchange for her vote or support.
Nonetheless, sources point out that Mr Varadkar has insisted that TDs be in the chamber for motion tomorrow night and rally around the embattled housing minister.
“But she would have to consider an awful lot of things if she votes or abstains. The Taoiseach has made it clear. You could probably take a good guess at what might happen,” said a Fine Gael official familiar with the details of the row and Ms Byrne's position.
A separate parliamentary party source said:
“That could be the end of her ministerial career. I can't see how she would do this over Eoghan.”