Hundreds of Asda supermarket staff on Wearside are beginning a three-day strike in a dispute over pay.
More than 500 members of the GMB union at the distribution centre in Washington are taking part in the action which began at midnight.
The GMB said the strike would be “solid” and would affect stores across the north of England. The walk-out is due to last 72 hours, after members were balloted and rejected the pay offer.
The union said its 530 members had been offered a 10% pay rise, but only if they gave up the right to collective bargaining, which they refused.
An Asda spokesman said customers would not “notice a thing” and that contingency plans were in place. He added the company had been in touch with the union by letter and was happy to work with them and with arbitration.