Air Canada CEO Mike Rousseau said on Monday the airline was "amazed" by the decision of its flight attendants' union to defy an order by the Canada Industrial Relations Board, which has declared the union's strike unlawful.

Air Canada flight attendants waved flags and held signs reading “would you work for free?” as they picketed outside Toronto’s Pearson International Airport on Monday.

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Air Canada has already begun canceling flights after hitting an impasse in contract negotiations with the flight attendants' union as a possible strike looms. Earlier this week, the union issued a notice of intention to strike,

After months of stalled negotiations, 10,000 Air Canada flight attendants walked off the job early Saturday morning. The federal government stepped in hours later to order binding arbitration, forcing an end to the strike — or so they thought.

Air Canada Chief Executive Mike Rousseau said on Monday that the airline was "amazed" by the decision of its flight attendants' union to defy the Canada Industrial Relations Board, which has declared the union's strike unlawful.