The executive of the Communication Workers' Union, however, decided to recommend a Yes vote in a strike ballot, rather than a referendum on the Royal Mail's peace formula with strong advice to accept.
Labour leaders nevertheless welcomed what they thought was a "sensible decision". An aide to Tony Blair said: "We are obviously delighted that the executive has agreed to ballot."
An internal memorandum from David Blunkett, Labour's Education and Employment spokesman, circulating among Shadow Cabinet ministers yesterday confirms the party's plans to introduce a mechanism for reballoting strikers on "substantial" fresh offers during industrial disputes.
It is now likely that ministers will withdraw their threat of a three month suspension of the Royal Mail's letters monopoly.
Alan Johnson, joint general secretary of the union, who has strong private misgivings about more disruption, said the CWU leadership would campaign for more strikes.
He denied that pressure from the leader of the Labour Party had brought a climbdown by the executive. Even if the 130,000 members rejected further action it did not mean they accepted the offer and the union would call for further negotiations, Mr Johnson said.
The Royal Mail has offered to set up a joint working party under the chairmanship of Acas, the conciliation service, to investigate management productivity plans.
The result of the ballot, which will cost the union pounds 80,000, will not be known until next month.