Ed Miliband faces a major attack on his leadership today as trade unions call on Labour's grassroots to reject public sector pay restraint.
The Labour leader is on a collision course with union bosses after backing the Government's salary freeze and arguing that protecting jobs was a higher priority.
The row will flare on the conference floor today when a union motion urges the party to condemn the policy, warning it amounts to a real-terms cut for workers and will fuel economic stagnation.
Mr Miliband told Len McCluskey, general secretary of Unite, he is "wrong" on pay restraint, insisting jobs must be top priority.
GMB leader Paul Kenny chose to aim his fire at Ed Balls, drawing up a dossier of "Balls Ups" he said were made when the shadow chancellor was in government.
Mr Kenny said of Mr Balls: "He would give an aspirin a headache, wouldn't he?"
Meanwhile, Lord Prescott told union leaders to "grow up" after Mr McCluskey said it was time to "kick the New Labour cuckoos out of our nest".
The internal wrangling comes at a time when the party is attempting to turn its fire on the coalition and present Ed Miliband as a credible future prime minister.
Mr McCluskey warned that Labour will lose the next election if it does not connect with workers, saying that the public sector pay freeze was also starting to have an impact on workers in private firms.
But Mr Miliband sought to use the row to show that the movement was not "pulling our strings". Asked about the pay row he told the BBC: "He is entitled to his view but he is wrong.
"We've got the right policy to say we put jobs in the public sector ahead of pay rises. That's what we said we would do this parliament. It is a difficult decision but it is the way to keep jobs in the public sector."
Shadow chancellor Ed Balls will today call for cash raised by selling off 4G mobile phone licences to be used to "kick-start the economy" by building 100,000 affordable homes and a tax break for first-time buyers.