Leadership candidate Liz Kendall has today hit back after a union leader described Blairites as a 'virus' in the Labour party.
Kendall, seen as the most Blairite in the Labour leadership contest, said the only antidote Labour needs is for the Tories.
Dave Ward, deputy general secretary of the Communication Workers' Union (CWU), today stood by his claims about Tony Blair's legacy to the party and his belief Jeremy Corbyn was the "antidote".
Mr Ward's union has endorsed left-winger Mr Corbyn for the Labour leadership.
He told the BBC Radio 4 Today programme: "The virus I am referring to is the policies and the approach of the likes of Peter Mandelson who seem to continuously push these sweeping statements that what this contest is all about is Labour winning an election, it's all about being credible, it's all about moving back to what he describes as the centre ground.
"All I am saying is we need within the Labour Party to have a fundamental debate on what the party stands for before we move back to those type of positions."
Mr Ward said Labour under Mr Blair had done good things, highlighting the minimum wage and reduced child poverty.
But he condemned other moves, such as introducing competition to his own industry, the postal system.
Mr Ward said: "The problem with the Blair side of the party, the Blairites which Peter Mandelson epitomises for me, is they never accept any of the bad things they have done."
He added: "I want to see a party that stands up for workers again, that stands up for the disadvantaged in society, and puts those principles first without compromising those principles just in pursuit of an election victory."
Mr Ward said it was "absolutely true" Labour had to win back Tory voters to stand any chance of election victory.
He added: "When I joined the Post Office in 1976, I got a job, I had a council flat, I had a good start in life to build my aspirations upon.
"The people who delivered that for me were the people who believed their values were in the centre ground of British politics. I personally think Labour has lost that type of core values and it promotes market competition in front of that.
"That has to be reversed - and you can convince the wider electorate they are the proper values the centre ground of British politics should be built upon."
Sir Ken Jackson, former general secretary of the group Amicus, told the same programme: "You have got to look at the realities of the situation.
"The Blairites won three elections, we had an expanding economy, we had full employment, inflation was under control, workers' rights were introduced by that government.
"I think yes, it wasn't perfect and there were things I could disagree with the Blairite government, but at the end of the day you have to achieve power, you have got to persuade people."
He added: "I don't know what Labour can do for working people when they are in permanent opposition."