Bus workers in County Durham and Teesside launched a series of 24-hour strikes on Monday at the Arriva company.
The workers, members of the T&G union, struck over the pay difference between drivers in County Durham and those in Northumberland.
Northumberland drivers are paid about £1 an hour more, according to the T&G.
Almost 900 drivers took part in the walkout.
If management fail to make a new, better offer, workers will strike again on Monday of next week and continue striking every Monday.