Air Canada flight attendants ’ strike entered its fourth day on Tuesday, causing widespread disruption for hundreds of thousands of summer travellers, despite the union confirming that talks with the airline have resumed.

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 the country's labor tribunal, but resumed talks seeking to end a walkout that has cancelled travel for half a million people worldwide.