Labour's newest TD Patrick Nulty has resigned from the party amid claims its cabinet ministers have brought the entire political system into disrepute.
The Dublin West TD, who lost the party whip for voting against the budget 18 months ago, accused senior members of sacrificing core social democratic demands for their own personal political ambitions.
The politician said his resignation was a difficult but necessary decision to make. "I no longer believe that membership of the party is of any assistance in advancing the political ideas which form the cornerstone of my value system," he said. "These ideas are social justice, equality and the creation of full employment with quality work in our society."
"I still have great regard for the many decent, hard-working Labour members, supporters and public representatives who share my thirst for a better Ireland.
"However, the leadership of the party, and in particular the cabinet ministers who have sacrificed core social democratic demands for their own personal political ambitions, have brought the entire political system into disrepute."
Four other TDs - including former junior minister Roisin Shortall, Colm Keaveney, Tommy Broughan and Willie Penrose - and MEP Nessa Childers also quit the parliamentary party since Labour took office in 2011.
Mr Nulty said trust in the political system has been broken. "This means there is a need for new ideas and social movements that are accountable to citizens, not powerful interests," he continued. The most recent example of the Government hitting the most vulnerable hardest is the announcement that children with special education needs will not receive the resource teaching hours they require next September.
"The Government has imposed savage cuts to housing adaptation grants specifically provided to people with disabilities who need alterations to their home. We have personal insolvency guidelines published which seek to micro-manage the personal finances of hard-pressed families and we have seen cuts to Child Benefit which Labour had sworn to protect.
"These are not the actions of a party that is acting in the interests of working people and a just economic recovery. I am optimistic about the future of our country and I will continue campaigning for the radical change that is needed."
Taoiseach Enda Kenny was not surprised by Mr Nulty's resignation. He added: "The deputy resigned from the Labour Party before, he has not been an avid supporter of the Government and people make up their own minds about things. The Government have a very clear programme for government that they have to implement, sort out the public finances and get our people back to work, and I am glad to say we are making very solid progress in that regard."