The Canada Industrial Relations Board had declared the strike illegal earlier on Monday and ordered the striking flight attendants back on the job. But the union said it will defy this second return to work order, after an earlier one had been ignored. The earlier one also ordered the union to submit to arbitration.

Air Canada’s flight attendants stayed on strike even after the country’s labor board ordered them back to work, causing the airline to delay plans to restart flights.

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