Paul Murphy told Newstalk Breakfast he does not see how Joe O'Toole can be impartial after interview comments
The head of the new commission on water charges is facing calls to step down.
Joe O'Toole - former senator and former president of ICTU - is under mounting pressure after saying the expert commission needs to find "a solution that will have enough sugar on it to make the medicine go down easily."
Mr O'Toole has issued a statement reassuring the public he is 'completely impartial' after criticism from opposition TDs.
He also says he will keep an 'open mind' and "engage with all interested parties during the course of the Commission’s work".
Stephen Donnelly of the Social Democrats says he believes Joe O'Toole position is ‘completely untenable’.
Talking to Newstalk Lunchtime, the Wicklow TD said: "He will have no choice but to step back. He should step back straight away.
"The public need to be absolutely confident that whoever is in the chair is going in there and saying 'I accept that there are very strongly held views and very different opinions, and we the commission will examine all of those credibly."
Earlier, Anti Austerity Alliance TD Paul Murphy said he does not see how Mr O'Toole can be impartial when he is clearly in favour of paying for water.
Mr O'Toole has taken part in a number of interviews since he was appointed, and Deputy Murphy told Newstalk Breakfast that the comments are inappropriate.
"In each of those interviews, he has come out strongly in favour of water charges," Deputy Murphy explained. "He's described those who oppose water charges as completely and utterly wrong on the issue.
"Most significantly, I think, was where he talked about what the commission was - he described it as a 'political exercise'".
Fianna Fáil TD Thomas Byrne says his party is looking for Mr O'Toole "to seriously reflect on his position".
"We in Fianna Fáil would have huge respect and regard for Joe O'Toole, and when he was appointed initially we would have been very happy with Joe," Deputy Byrne said.
"However he has expressed fairly strong and robust views since his appointment, and I think that makes it very, very difficult for him at this stage."