Independent TD for Louth Peter Fitzpatrick has said he will not be supporting the Government in Tuesday's no confidence vote in the Housing Minister Eoghan Murphy.
His decision puts yet more pressure on Government, as they struggle for numbers ahead of the crucial vote.
The Social Democrats have tabled a vote on the embattled minister, who dismissed the motion as a 'stunt'.
However, Fianna Fáil confirmed last week it will not support the motion.
Minister Murphy previously survived a no confidence motion from Sinn Féin in September 2018.
The latest move caught the Government off guard, as they were not expecting a vote of confidence or anything like it this close to Christmas.
Social Democrats co-leader Catherine Murphy has said she believes some people do want do go to the polls, even if it means a general election in the days after Christmas.
She argued: "There is a real anger - we can't keep postponing this.
"This is not about us, this is not about Dáil arithmetic - this is about a really critical issue that we can't postpone any longer."
And speaking on The Hard Shoulder on Monday, Deputy Fitzpatrick said: "I will not be supporting Eoghan Murphy tomorrow night".
Asked if that meant he would be voting against him, Mr Fitzpatrick added: "I will, yes".