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.

Striking Air Canada flight attendants vowed Monday to defy another back-to-work order from Canada's labor tribunal, extending a work stoppage that has cancelled travel for half a million people worldwide.

The union representing Air Canada flight attendants vowed to fight a federal order to end their strike, calling it "blatantly unconstitutional" and accusing the government of siding with the airline.