Independent TD Finian McGrath last night withdrew his support from the Government as a result of the proposal to remove automatic entitlement to medical cards for the over-70s.
At a press conference in Dublin Mr McGrath also signalled that he would vote against the Government when the Fine Gael private members' motion opposing the medical card proposal is put before the Dáil on Wednesday.
Mr McGrath's withdrawal of support was widely anticipated since the weekend, when he signalled that the removal of medical cards from pensioners was unacceptable and unpalatable.
On Friday, Mr McGrath met the Minister for Health, Mary Harney, and said afterwards that he was prepared to see the compromise the Government would propose.
However, by Saturday he had hardened his position to say that he would withdraw his support unless the scheme was scrapped in its entirety.
Making his announcement last night, Mr McGrath, a deputy for Dublin North Central, said: "I am not going to beat around the bush. I am here to announce my withdrawal from supporting the Government."
He said that the medical card issue was the primary reason that guided his decision. "Tinkering around with the issue is not an option. I am calling for a total reversal. I have talked to our senior citizens and listened to them."
His letter to Taoiseach Brian Cowen was also released last night. He said he would vote on each issue as it arises and that his decision had come after waiting patiently for the Government to reverse the decision for a few days.
"I have always supported the call for more patriotism. However, my patriotism does not include hammering the elderly, the sick the disabled and young children in large classes."
He also signalled the possible re-establishment of a technical group in the Dáil, comprising Sinn Féin, Tony Gregory, himself and Joe Behan. He said he would be talking to Mr Behan today.
On his contacts with the Government, he said he had spoken to Mr Cowen's programme manager, Joe Lennon, yesterday to inform him of his decision.
He agreed he had changed his position between Friday and Saturday morning but denied it had anything to do with Joe Behan's resignation from Fianna Fáil.
"What influenced me was listening to people and talking to constituents for five hours on Saturday morning. This was also the way my election workers wanted to go. I did change ground," he said. Mr McGrath also read out a list of the projects that had been completed in his constituency as a result of his deal with Fianna Fáil.