Green Party TD Neasa Hourigan resigned as party whip before she voted against the Government on legislation that extended the rent freeze and eviction ban only for those affected by Covid-19.
Ms Hourigan voted in favour of a Labour Party amendment that would have extended the legislation to all tenants.
Green Minister Joe O'Brien also abstained during the vote on the same legislation, raising serious concerns about his position in the party.
However, he is not expected to resign his ministry.
The Green Party is understood to be considering suspending both Mr O'Brien and Ms Hourigan for not voting with the Government.
Ms Hourigan confirmed to the Irish Independent she resigned as whip before the vote and wrote to her executive council to tell them of her decision. She plans to stay in the party but said it was up to the parliamentary party to decide the next step.
Speaking to the Irish Independent, 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."
Mr O'Brien did not respond to requests for comment on his decision to abstain on legislation brought before the Dáil by his constituency colleague, Housing Minister Darragh O'Brien.
Fianna Fail and Fine Gael TDs were furious over the lack of support from their Green colleagues.
A Cabinet minister said: "Not good, particularly not a minister of State refusing to support government legislation."
Junior Minister Mr O'Brien yesterday evening explained his decision on Twitter saying: "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."
Meanwhile, Tánaiste Leo Varadkar ordered a security review for a State car and Garda driver for Foreign Affairs Simon Coveney in his final days as Taoiseach.
In one of his last acts as Taoiseach, Mr Varadkar ensured Mr Coveney retained his taxpayer-funded security detail before the new Government was formed.
Mr Coveney was due to lose his car and driver after he stepped down as Tánaiste.
In the days before Mr Varadkar was succeeded by Fianna Fáil leader Micheál Martin, the then-taoiseach contacted his department's secretary general Martin Fraser to ask for the security review.
But Mr Fraser did not officially ask his counterpart in the Department of Justice, Aidan O'Driscoll, for the review until the day after Mr Martin was appointed Taoiseach.
Mr Martin was not alerted to Mr Fraser's decision to obtain security advice that ensured Mr Coveney retained his €200,000-a-year State car and driver.
It's not that they're all not getting along. Most politicians involved in the calamity Coalition will tell you they are all getting on famously despite all the preconceived differences they might have.