Unison, the second largest trade union in the country, has backed Jeremy Corbyn for Labour leader after a consultation with members.
More than 20,000 union members responded to an online poll, with 48 per cent opting for Corbyn.
Corbyn said he was “proud” to have their support:, and pledged to end the public sector pay cap overnight.
Unison represents 1.3million workers providing public services. General secretary Dave Prentis said: “Jeremy Corbyn retains the backing of a majority of Unison’s Labour supporting members. That’s why the committee supported his nomination again.
“However, a significant minority backed Owen Smith. Their views will always be respected in our union- that’s our proud tradition.”
He warned against “toxic” abuse, threats and aggressive language during the contest and called for a united opposition.
“Labour is in danger of becoming the new ‘nasty party’ if this behaviour continues unchecked,” he said. “There’s no place in the party for witch hunts against MPs, councillors and party staff.”
Unite, the other heavyweight, has also backed Corbyn, but it did not consult members first. The general secretary Len McCluskey had been vocal in his support for the embattled Labour leader.
Nevertheless, Unison’s decision to back Corbyn will come as a blow to the challenger, Owen Smith. There was hope in the anti-Corbyn camp that union voters could back them after members of another union, the GMB, opted for Smith over Corbyn.