Air Canada flight attendants remained on strike Sunday, defying a government labor board’s order to return to work and forcing Canada’s largest airline to delay its restart plans.

Air Canada said it suspended plans to restart operations on Sunday after the union representing 10,000 flight attendants said it will defy a return to work order.

The shutdown of Canada’s largest airline early Saturday is impacting about 130,000 people a day, and some 25,000 Canadians may be stranded.