Labour's shadow chancellor Ed Balls endured heckling and hostility as he faced up to union members at the TUC conference in Brighton.
Delegates shouted "shame on you!" as he struggled to answer a question about anti-union striking laws.
When he said that Labour would have been forced to impose spending cuts some members of the audience called out: "Rubbish!"
Britain's trade unions are deeply suspicion of the Labour leadership, after Ed Miliband warned them yesterday against opposing the coalition's cuts with wide-ranging industrial action.
One Unison delegate who told Balls that he couldn't afford a pay freeze was greeted with applause from the conference floor.
Further applause met the Public and Commercial Service union's president Janice Godrich when she told Balls that his support for the government's pay freeze was "deeply disappointing".
Balls had argued in his speech that it was difficult for the opposition to "reverse particular tax rises or spending cuts" because Labour did not know what it would inherit if it won the 2015 general election.
The shadow chancellor used his speech to underline Miliband's opposition to strikes as the best means of taking on the coaltion's austerity drive.
"You say that strikes must always be a last resort. And I am sure that the last thing the vast majority of trade union members want, at a time of such uncertainty, is strikes over the coming months," Balls said.
"It is not what we want. It is not what the public wants either. But when coalition ministers warn that they will have to act and legislate if we see a return to the un-rest of the 1980s, what we are really seeing is Tories itching to provoke a row about strikes so they can blame the stalling recovery on trade union members and working people."
Balls urged against a "return to the hatred, division and confrontation of the 1980s", adding: "We don't want a return to the strikes and lost working days of the 1980s – seven times more days lost than under the last Labour government."