Talks will be held next week in a bid to avert another damaging postal strike in Oxford.
But if they are not successful, union leaders have been given permission to press ahead with a ballot for official industrial action after clashing with bosses over new holiday arrangements.
Steve Peck, spokesman for the Oxford branch of the Communication Workers Union, said: "This will be a serious attempt to resolve this dispute -- if it doesn't work then we will implement the ballot."
The row centres on a new rota which drawn up by managers.
Union leaders say their alternative was not considered, which was in breach of an agreement drawn up at the end of the last strike in November.
Royal Mail spokesman Richard Smith said: "We welcome all dialogue."
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