More than 1,000 Stagecoach drivers in Manchester are to be balloted for industrial action over pay.
Unite has said the employees have rejected an offer of 4% from June this year with a further 4% in December.
The union argued that the offer would be a real terms pay cut.
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Unite general secretary Sharon Graham said: "Stagecoach is a hugely profitable company. The money is there for the company to provide its Manchester drivers a pay increase that reflects increasing living costs and the demands of what is a difficult and stressful role.
"Improving jobs, pay and conditions is Unite's absolute priority and our Manchester Stagecoach members will receive the union’s complete support."
The ballot for strike action opens today (July 6) and closes on July 27. Unite said that strike action would "severely impact" bus services across the whole of Manchester.
Unite regional officer Colin Hayden added: "Stagecoach can prevent this dispute from escalating by putting forward an offer that our hardworking members can accept.
"Unite urges Stagecoach to return to negotiations and table a deal that improves on the inadequate one currently on offer."
A Stagecoach spokesperson said: "We have further talks already planned and are committed to continue to work constructively with Unite to deliver proposals that are fair."
