OTTAWA, Ontario — The union representing Air Canada’s 10,000 flight attendants said Sunday that it would defy the government’s back-to-work order and continue a strike that shut down Canada’s dominant carrier and severely disrupted travel throughout the country.

The announcement came at the same time that Air Canada had ordered the flight attendants to show up for work Sunday afternoon to restart service that evening.

“We will be challenging this blatantly unconstitutional order that violates the charter rights of 10,000 flight attendants, 70 percent of whom are women, and 100 percent of whom are forced to do hours of unpaid work by their employer every time they come to work,” the Canadian Union of Public Employees said in statement. “We remain on strike. We demand a fair, negotiated co

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