Labour leader Brendan Howlin has said he would be "happy to sit down" with Sinn Féin and discuss working in government as part of an alliance of left-wing parties.
Speaking after a leaders TV debate in Galway on Monday night, Mr Howlin outlined what is now being viewed as a significant shift in Labour policy in cooperating with Sinn Féin.
Some former elected figures in the party have also taken issue with the decision.
Asked by journalists about working with Mary Lou McDonald's party in power, Mr Howlin said:
“There's two phases in that. I think one of the mistakes all of us in the left made in the past is we were picked off, attacking each other. The Greens went into government with Fianna Fáil and they were demolished. We went into government and we were demolished.
“We need to have an alliance of progressive thinkers who could set out a platform of investment to solve this crisis. Once we have that, I'm happy to sit down with Sinn Féin.”
“I'm happy to sit down with Sinn Féin but the caveat I've entertered and I entered this on every occasion, is there is a fundamental issue of trust. Now I have served in government and it collapsed on the basis of trust, government, between different parties, only can survive on the basis of trusting one another.”
He went on to explain that that trust issue was an "impediment" to working with Sinn Féin.
It is an issue that Sinn Féin has to address and overcome.
He pointed to the RTE Claire Byrne Live leaders debate which included claims from other leaders that Sinn fein policy was decided by its Ard Chomhairle, a party government body which includes unelected officials. However, Ms McDonald told the 300-strong audience on the night that the body was "no different to the GAA".
But Mr Howlin still has concerns. He added:
“Our Cabinet system under the constitution can't work like that.
“Ministers can't take instructions from people other than the people who sit around a constitutional government. That has to be addressed. I'd have a difficulty, unless that was addressed.”
But asked again by reporters at the NUI Galway debate whether, if this was addressed, Labour would then open to the door to talks with Sinn Féin after the election, Mr Howlin responded:
“I would sit down and talk with anybody in terms of what we can do. But the trust issue is a fundamental one.”
Responding, former Labour senator Mairia Cahill questioned Mr Howlin's position on the issue. She tweeted there was still an "IRA hierarchy" in Sinn Féin and there was the party's "magic bean economy", among matters.
Mr Howlin's comments also come after Ms McDonald said she was willing to talk to other parties after the election on the left and also after People Before Profit TD Richard Boyd Barrett called for a grand coalition of the left to join forces, in order to prevent Fine Gael or Fianna Fáil returning to power.