Two further strikes are planned by bus drivers
Bus drivers in South Yorkshire are staging the first of three planned strikes in a row over pay.
Stagecoach services in Barnsley, Rotherham and the Dearne Valley are affected by Monday's walkout.
Stagecoach said it was bringing in drivers and managers from other areas to deal with the industrial action.
A Stagecoach Yorkshire spokeswoman said services would run "as near to normal" as possible during the day. Some disruption is expected after 1800 GMT.
School bus services are not affected by the strike.
A planned strike by Stagecoach drivers in Barnsley has been cancelled, but bus drivers in the town are planning to take part in the two further strikes on 30 November and 7 December.
The Stagecoach spokeswoman said the dispute had been ongoing since April.
She said several pay offers had been made to the drivers, including one which the union had recommended its members accept, but they had been rejected.
The company operates a number of local bus services in South Yorkshire,
Bus drivers from separate company First have cancelled all strike action in South Yorkshire after entering into talks with management.
The First workers were unhappy over the company's handling of some disciplinary issues at Sheffield's Olive Grove depot.