Fianna Fail leader Micheal Martin said Fine Gael's Dara Murphy should have resigned when he took up a full-time role with the European People's Party in 2017.
He said the former junior European Affairs minister had "essentially disappeared for two years and that is not good enough."
Speaking in Leinster House, Mr Martin said Mr Murphy neglected his duties on behalf of the people of Cork North-Central and said the Taoiseach was wrong to facilitate the situation.
He said Mr Murphy has had virtually no input in terms of being a representative and said he should consider fully "how he has handled things".
As he welcomed his two newly-elected TDs – Malcolm Byrne of Wexford and Padraig O'Sullivan of Cork North-Central – on their first day in the Dail, Mr Martin also said that Easter is the best cut-off point for a General Election.
Pressed by reporters about how much longer this Dail can last, Mr Martin said he has not spoken to the Taoiseach about agreeing a date to call an election, but in his view Easter is the most appropriate time.
Mr Martin dismissed as a “stunt” the calling by the Social Democrats of a motion of no-confidence in Housing Minister Eoghan Murphy and that there was never any chance of his party doing anything other than abstaining.
“Let's be straight, nobody expected this motion to pass tonight. I certainly didn't and don't for obvious reasons. The Social Democrats tabled the motion in the middle of a by-election, that is their prerogative.”
“I don't think anyone is serious about there being a General Election anywhere around Christmas Day. Certainly, the public would not have been thankful for that.
“I have been clear about the trajectory of this Dail. We did not get enough seats at the last General Election [to form a Government]. We stood up to the plate and facilitated the formation of a Government on the basis of policy. It has to be based on policy,” he said.
“Clearly, the Government has failed on Health and Housing. I said a couple of weeks ago that I felt that Easter was the natural cut-off point for this parliament,” he added.
He said his party was right not to pull the plug on the Government in light of the continuing uncertainty around Brexit.
Mr Martin said he does not want Eoghan Murphy “getting off the hook” and he wants him and Simon Harris to go before the people to “defend their failure.”
He also played down the chances of TDs Niall Collins and Timmy Dooley of returning to this front bench before the General Election.
Mr Martin also cautioned against proposals to stop TDs from having second jobs, saying parliament is at its best when a range of expertise is present in the Dail.
The two new TDs, spoke to the media, and said they were looking forward to getting to work, with Mr Byrne joking he hoped the Government does not collapse on their first day.
“I hope it is not decided tonight, I don't really want to be on a fourth election ballot paper before Christmas. People do want a change of Government,” Mr Byrne said.
Mr O'Sullivan said he no longer feels Fianna Fail is “indicative of the corrupt, self-serving politicians we have and the out-dated system they represent.
They were views he expressed when he was an independent candidate before he joined Fianna Fail.
He said he has since contested three elections for the party and is looking forward to spending the day in Leinster House with his family.