Green Party TD Neasa Hourigan resigned as party whip before she voted against the Government on legislation which only extended the rent freeze and eviction ban for those impacted by Covid-19.
Ms Hourigan voted in favour of a Labour Party amendment which would have extended the legislation to all tenants.
Junior minister Joe O’Brien also broke ranks with coalition colleagues and abstained from the main vote on the government’s own Bill.
Ms Hourigan confirmed to Independent.ie she resigned as whip before the vote and wrote to her executive council to tell them of her decision.
The Dublin Central TD plans to stay in the party but said it is up to the parliamentary party to decide the next step.
Speaking to Independent.ie, Ms Hourigan said: "I have significant concerns as to the impact of this legislation on levels of homelessness across the State.
"I do not believe it takes into account the scale of the coronavirus pandemic and the need to keep people safe in their homes. Eviction due to sale is directly in conflict with Green Party policy and so I am unable to support this bill," she added.
Fianna Fail and Fine Gael TDs were furious over the lack of support from their Green colleagues.
A senior Fine Gael source said: "We all thought she'd make it as far as the Budget.
"They're all mad for the place to end now tonight," the source added.
A Cabinet minister said: "Not good, particularly not a minister of state refusing to support government legislation."
Housing Minister Darragh O’Brien rushed legislation through the Dáil which will extend the rent freeze and eviction ban until January 2021 – but only for those who self-declare they have been impacted by the coronavirus pandemic.
Mr O’Brien previously promised to extend the rent freeze until at least October but U-turned on this once he was appointed minister.
This is the first time Ms Hourigan, who opposed entering into government with Fianna Fáil and Fine Gael, voted against the Government.
The Dublin Central TD is a founding member of a Green Party affiliate group, Just Transition Groups, who have spoken out against the Government since they were formed.
Junior Minister Joe O’Brien this evening explained his decision to abstain from the Dáil vote.
He said on Twitter: “The issue of homelessness is an extremely important one for me.
“I’ve worked in the area, I’ve been a whistleblower in the area, I have friends who work in the NGOs and I feel we need to do everything we can to tackle it.
“I’m elected in part to be a legislator.
“I wasn’t convinced that this piece of legislation was the best we could have done in what are, to be fair, unusual circumstances.
“This was mainly due to its extremely rushed nature.
“I had read enough and heard enough to make it clear to me that it could have been stronger in terms of preventing and reducing homelessness. “The issue here was not dedicating sufficient time to a piece of legislation that could have profound consequences on people's lives,” he said.
The Dublin Fingal TD added: “I knew my vote was not going to defeat the Bill but I felt I also had to give a signal that how it was done was not good enough.”