Their union says one of its core demands, to receive pay for groundwork, is unlikely to be introduced in arbitration. The airline began canceling flights ahead of the potential strike.

A complete shutdown of Air Canada is looming if the union representing the flight attendants of the country’s dominant air carrier and the airline fail to reach an agreement within hours.

The prospect of a systemwide work stoppage by Air Canada's unionized flight attendants loomed large on Friday with a strike deadline just hours away, despite a government plea for the two sides to return to the bargaining table.