The Green Party has suspended and removed the party whip from TDs Neasa Hourigan and Patrick Costello.
The parliamentary party agreed the sanctions after the pair voted against the Government in the Dáil last night.
They backed a Sinn Fein motion calling for the National Maternity Hospital to be built on public land.
Both TDs can apply for readmission to the party in six months’ time.
It means the Government’s Dáil majority has been reduced to just one vote – with Fianna Fáil, Fine Gael and Green combined now commanding just 80 votes.
There are 160 TDs in the Dáil; however, the Ceann Comhairle doesn’t vote unless the house is tied – meaning the Government retains a slight majority.
Green Party Chair Senator Pauline O'Reilly told Newstalk the sanctions were necessary.
“A decision was taken last night following the vote to suspend Deputy Hourigan and Deputy Costello from the parliamentary party and to remove the whip for a period of six months,” she said.
“We regret having to take this decision, but it is very important to have unity when it comes to voting to remain a force within Government.”
Senator O'Reilly said the party understands the rogue TDs point of view.
“We would have preferred to have seen the National Maternity Hospital built on public land; however, that land simply wasn’t for sale,” she said.
“So, while we understand this is a difficult issue for some, it is important the Government acts as one.”
In a statement, Deputy Costello said he had no choice but to vote against the Government.
“I know this is frustrating for our government partners, but the issue of the National Maternity Hospital has been incredibly frustrating, confusing and challenging for many,” he said.
“This motion reflected my own concerns and the concerns of many. I could not in good conscience vote against it.
“I know breaking the whip is a serious issue and as I have said earlier, I will accept the sanctions imposed from my action.”
The Green Party previously sanctioned Deputy Hourigan and Minister of State Joe O’Brien for failing to vote with the Government on the Residential Tenancies Bill.
The deputies had their speaking rights removed for two months but they were not suspended and kept the party whip.
It is believed the party was facing pressure from its Government partners to take stronger action this time around, with the Tánaiste Leo Varadkar telling Newstalk yesterday that sanctions against TDs who voted against the Government were “inevitable”.
The Green Party said it regrets having to suspend the two TDs but “our effectiveness in government relies on unity in every vote”.
It said the decision was reached by consensus.