The industrial action started on Monday and will last “for an undisclosed period”, the union says.
Arriva buses across parts of Yorkshire have been suspended due to drivers going on strike in a pay dispute.
The industrial action by Unite members started at 02:00 BST and is to last for “for an undisclosed period of time”.
Phil Bown, from the union, apologised for the disruption to passengers but said workers wanted an “inflation-related pay increase of around 10%”.
Arriva said its offer was a “significant increase” and described the strike action as “unjustified”.
Mr Bown said the pay dispute had been going on for more than eight months and that Arriva had offered between 7% and 12%, but most workers would receive the lower end of pay rise which would be 3% below the current inflation rate.
“I’ve got bus drivers here who are working 40 to 50 hours a week can’t afford to live on the cost of living that they are,” he said.
“Some of them are going to food banks to subsidise their income, they shouldn’t have to do that – they’re full-time workers.”
Gavin Peace, from Arriva, said he was “extremely disappointed” at the strike.
“Arriva offered a substantially improved pay offer which Unite are refusing to ballot their members on,” he said.
“This isn’t fair to our employees and communities across Yorkshire who want this issue resolved. The strike should be immediately suspended while Unite’s members vote on the fair and generous offer.”
The bus firm said it would be unable to operate services across Wakefield, Dewsbury, Castleford, Pontefract, Heckmondwike, Cleckheaton, Bradford, Leeds, Ossett, Batley, Morley, Rothwell, South Elmsall, Hemsworth, Huddersfield, Halifax, Doncaster, Selby, York and Goole.
It added that Arriva North East bus services, which operate into North Yorkshire, were not affected.
Arriva said pre-paid tickets would be accepted on First Bus and Transdev buses.
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