Labour Party Chairman Colm Keaveney has resigned from the party.
In a statement at Leinster House, Mr Keaveney said he could no longer go along with what he said was "increasingly like a political charade".
He said Labour promises one thing, then does another and blames it on someone else.
Members, he said, must accept what they are given and the leadership will tolerate no dissent.
The East Galway TD said it was with a heavy heart that he was forced to reach the only decision he believed to be honourable, and resign as chairman and from the party itself.
He said he would continue to represent the people of his constituency and would not breach the contract they made with him just for the sake of staying in a position.
Too many at the Cabinet table are "willing to trade what they held dear for one more hour in the sun", he said.
Mr Keaveney had lost the whip after voting against the Government on education cuts.
He has been a consistent critic of the party's performance in Government.
Some recent Govt decisions 'odious'
Mr Keaveney said the final straw for him was his inability to communicate with Minister for Education Ruairi Quinn over cuts to special needs education in recent days.
He said there was little point in being chair of the Labour Party when you are ignored by Labour ministers when attempting to defend vulnerable people.
He described some recent Government decisions as "odious" and as "flying in the face of our value system".
Mr Keaveney said there would probably be a cork popped in Iveagh House (Department of Foreign Affairs) at news of his departure.
He said he would not want to be accused of interfering with Tánaiste Eamon Gilmore's "project" for the Labour Party, saying that he had been a convenient excuse for too long.
Mr Keaveney said the party needed to reassess the Programme for Government and to consider whether Mr Gilmore was the best person to lead Labour into the next election.
Dowds 'disgusted' by Keaveney's decision
Labour Party TD for Dublin Mid West Robert Dowds said he was disgusted by Mr Keaveney's decision.
He accused him of cowardice and not being willing to face up to the tough decisions that had to be taken by the Government.
Mr Dowds said that when Mr Keaveney was elected Chairman of the Labour Party he put himself up as a conduit between the parliamentary party and the membership, and he had let people down by his actions.
Mr Keaveney's resignation has been welcomed by his former party colleague Emmet Stagg.
Mr Stagg said Mr Keaveney had "consistently attacked Labour" since losing the whip and had betrayed party members who had elected him as chairman.
Today's resignation marks the second time Mr Keaveney has resigned from the party.
He stood for the party in the Galway East constituency in May 2007 and failed to get elected with just over 3% of the first preference vote.
A few weeks later, he resigned in protest over Pat Rabbitte's leadership.
He rejoined the party in June 2008 and remained a member until today.