Gerry Adams has said it was a mistake for Siptu to urge its 200,000 members to vote for Labour.
He claimed his political rivals had betrayed the working class.
The union abandoned its once in a century hope for a left-wing government and encouraged its 200,000 members to vote for Labour, as a restraint on a Fine Gael-led government.
The Sinn Fein president canvassed in Dun Laoghaire today – entering the award-winning Monkstown boxing club ring with a swift dart under the ropes.
The gloves were off as he attacked his political opponents.
“It is certainly a mistake to call upon voters to vote for Labour, given the record of Labour, who have betrayed the working class. I think it will go down very, very badly with a lot of Siptu members.”
Mr Adams toured Mounttown in Monkstown, a smart estate in south Dublin with inquisitive children on scooters and a largely receptive adult audience unhappy about the standard of public housing provision.
Ballymun-style tower blocks have long since been demolished and the Mounttown community centre is home to an award-winning boxing club among others.
Mr Adams, a former amateur, climbed into the ring for a photograph with the team.
He said: “I was not very good, I kept getting my glasses broken but I do think it was a brilliant character-building sport and discipline.”
He became philosophical.
“Everybody in their lives will meet somebody, some adult who changes your life, a parent, uncle, aunt, teacher, boxing trainer.
“All of you young men and women have the right to live your life to the full potential, to be happy with your lives and to whatever you want in your lives.”
On the doorsteps, one mother of six children aged under 10 bemoaned her cramped terraced house accommodation after a fire forced her from her home in Carrickmines.
Lindsey O’Brien, 29, claimed more attention was given to rehousing members of the Travelling community after the devastating blaze which killed 10 at a halting site in Carrickmines.
She said: “They say they do things for you but they don’t do nothing for you.
“It took me to have a special needs baby to get a house.
“I have never dealt with Sinn Fein but hopefully they might do something for me if I vote for them.”
Mr Adams claimed there was growing panic within Labour, Fine Gael and Fianna Fail, which were trying to get people to decide how they will vote through fear.
“People need to vote through hope, people need to be empowering themselves and not be put off.”
He said there had been a realignment of Irish politics.
“All of this takes time, you don’t just go from the old domination by Fine Gael and Fianna Fail since partition into a new dispensation but it is happening, and it is happening across Europe, it is even happening at the minute in Britain.
“It has happened in the North already, with the support that Sinn Fein get there, and it is starting to happen in this state.
“This is the first time in my lifetime that people will have the opportunity to elect a progressive government which is bedded in core values of republicanism, of citizens’ rights, of public service and all that citizens should have as a matter of birth right in the Republic.”