Two groups of bus workers in the T&G union have voted to reject pay offers.
At Yorkshire Coastliner, which operates routes around York and the North Yorkshire coast, workers rejected an offer of 4.8 percent and are currently balloting for industrial action.
Meanwhile around 1,000 workers at First Bus in Leeds have rejected the latest pay offer from their company and are set to reballot on an improved offer on 22 February.
The First Bus workers won concessions from management earlier this year after a strike last December against attacks on their pensions.
Yorkshire Coastliner has been the most profitable bus operator in Britain for the last four years. The company is owned by the multinational Transdev, which had an operating profit of £530 million in 2005.
First Bus made £92.2 million profits in the first six months of last year. Last week the company came into conflict with the Teamsters union in the US after First Bus bought the US company Laidlaw – the biggest operator of school buses in the US.