Unite union said it was taking action because Birkenhead Stagecoach drivers earn £2.69 an hour less than Arriva drivers in the town, and £2.13 an hour more than Stagecoach drivers in Chorley and Preston.
Unite general secretary Sharon Graham said Stagecoach “can absolutely afford to table an offer that tackles the unfair disparities within the region”.
“Stagecoach drivers at Birkenhead, Chorley and Preston will receive Unite’s full support in taking strike action until that happens,” she said.
The union said Stagecoach is “a highly profitable firm, with figures from last year showing it recorded a total operating profit of £51.1m – up from £33.1m – and a profit before taxation of £47.6m”.
Unite regional officer Mike Woods said: “Stagecoach is entirely responsible for the disruption that will be caused.
“It could have put forward an offer that addresses our members’ legitimate concerns but has refused to.
“Industrial action can still be avoided but that will require Stagecoach tabling an acceptable offer.”
Matt Davies, Managing Director of Stagecoach Merseyside and South Lancashire, said:
“We have worked closely with union representatives to try to agree a pay deal.
“Throughout this process, we have done our utmost to present an offer that meets their expectations whilst also being affordable for the long-term sustainability of the region’s bus network.
“We will continue to work constructively to reach a resolution.”
He said contingency plans were being prepared “to operate as many services for our customers as possible” and more information would be on the Stagecoach website.