The GMB union has thrown its weight behind demands for a referendum on Theresa May’s final Brexit deal.
Tim Roache, the general secretary of the union, said on Tuesday “Tory hard Brexit would be a disaster”.
The prime minister has ruled out holding another vote. But the union’s decision will increase pressure on Jeremy Corbyn to back another referendum.
Labour has said it is currently keeping its “options open” on whether to back a public vote.
The GMB is the UK’s third largest union, with almost 640,000 members and is a significant donor to the Labour Party.
In a video statement posted online, Roache said: “The promises that were made during the referendum campaign are simply not the reality we are facing.
“GMB respects the result of the referendum but how we leave he EU is as important as the decision to leave in the fist place.
“GMB is calling for a public vote on the final deal,” he added. “As trade unionists when we negotiate a pay deal with an employer we go back to our members and ask them if they are happy with it.”
Earlier in the summer the TSSA union also voted overwhelmingly to campaign in favour of a referendum on any Brexit deal agreed by Parliament.
The TUC annual congress in Manchester this weekend is also expected to see further calls for Labour to back another referendum.