Ed Miliband received a frosty reception from the unions on Tuesday when warned they risked irrelevance if they decided to strike.
The Labour leader was heckled by delegates at the TUC conference in London when he said teachers and civil servants had been wrong to stage industrial action in June over pensions.
"Strikes are always the consequence of failure. Failure on all sides. Failure we cannot afford as a nation. Instead your real role is as partners in the new economy," he said.
"You know you'll never have relevence if you allow yourself to be painted as opponants of change. In this new eoncomy you must be the agents of change."
He told delegates: "The best thing that can be done to avoid industrial action happening is by having a government willing to negotiate."
Miliband said he hoped the union link with Labour was "mature enough" to deal with disagreement but he was heckled by some delegates for his failure to endorse future strikes by the unions.
The TUC is due to back calls for an "autumn of discontent" to resist public spending cuts, with strikes planned for October and November.
He was also greeted with some shouts of "shame" for endorsing academy schools.
A report published yesterday resurrected the debate over whether Miliband was overly indebted to the unions after their support proved crucial in helping him to clinch victory in the Labour leadership contest.
However his bumpy ride in front of the delegates may help him distance himself from those accusations.