Air Canada Cargo is operating a temporary freighter schedule to mitigate the disruption, offering capacity to several airports across the U.S., Mexico, South America and Europe.

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.