Hundreds of bus drivers are staging their first in a series of strikes in a long-running row over working hours.
More than 375 Six Wilts and Dorset bus company drivers were walking out at midnight after talks failed.
The Rail, Maritime and Transport Union members at the Blandford, Bournemouth, Lymington, Poole, Ringwood and Swanage depots will strike for 24 hours in a protest against "excessive" working hours and are planning further walkouts on 8, 16 and 21 January.
Bob Crow, RMT general secretary, said:
"We suspended action in the summer in good faith to talk, but right up to last Thursday's meeting the company has failed to budge an inch and has continued to impose rosters," he said.
"Our members have voted twice by ten-to-one margins to take action over what is a simple issue of the health and safety.
"The company might think that is acceptable for drivers responsible for passenger safety to drive for more than four-and-a-half hours without a break, but we do not and I would hope that most Wilts and Dorset passengers don't either."
