Air Canada cancelled hundreds of additional flights on Sunday after the union representing its flight attendants announced the workers would remain on strike in defiance of a back-to-work order.
The Canadian Union of Public Employees said it filed a challenge in Federal Court on Sunday to an order by the Canada Industrial Relations Board that said its members must return to work by 2 p.m. ET.
"Our members are not going back to work," CUPE national president Mark Hancock said outside Toronto's Pearson Airport. "We are saying no."
Hancock ripped up a copy of the back-to-work order outside the airport's departures terminal, where union members continued picketing on Sunday morning as a way to signal to Air Canada that "we're ready for a big fight."
The federal government intervened in the labour dispute on Saturday, less than 12 hours after flight attendants initiated their strike.
Federal Jobs Minister Patty Hajdu said she was invoking Section 107 of the Labour Code to ask the Canada Industrial Relations Board to send the two sides to binding arbitration and order the airline and its flight attendants back to work in the meantime.
Hajdu told reporters the "potential for immediate negative impact on Canadians and our economy is simply too great."
The Liberal government has used this mechanism to intervene in a number of labour disputes, including a lockout and strike at the country's largest railyards in August last year.
On Sunday afternoon, Hadju's office said she was still monitoring the flight attendants' situation.
The airline said in a separate Sunday statement that CUPE has "illegally directed its flight attendant members to defy a direction" from the industrial relations board by calling for a "day of action" on Sunday.
CUPE held demonstrations outside of the Toronto, Montreal, Vancouver and Calgary airports.
CUPE has accused Hajdu of caving to Air Canada's demands.
Air Canada said Sunday it would push back its plan to resume flights until Monday evening, though the union said it will remain on strike until it has a "fair, negotiated collective agreement."
The airline did not immediately respond to questions about why it believed operations could resume by Monday.
Air Canada reported roughly 940 cancelled Air Canada and Air Canada Rouge flights during the work stoppage as of Sunday.
The cancellations left thousands of passengers stranded or struggling to find ways to reach their destinations.
Audrey Allen is one of them.
She said her 6 p.m. flight from Toronto to London, England, was listed as "on time" when she left for the airport Sunday afternoon, but by the time she set foot inside the terminal it had been cancelled.
Allen was planning to help care for a friend for three weeks, and was left scrambling to find a new flight in time.
"I don't know what's going to happen to her, because she can't afford to stay in this nursing home," she said, holding back tears. "And I can't do anything about it at all."
The CIRB order on Saturday stated that the terms of the collective agreement between the union and the airline, which expired on March 31, were to be extended until a new agreement was reached.
Hancock said the union received notice from the board late Saturday, informing them of the impending return to work. He said the union felt the "whole process has been unfair."
"Air Canada has really refused to bargain with us...because they knew this government would come in on their white horse and try and save the day," he said.
The union has said its main sticking points revolve around wages that have been outpaced by inflation during its previous 10-year contract, along with unpaid labour when planes aren't in the air.
Natasha Stea, the president of the local 4091 for flight attendants based in Montreal, said the workers supported defying the back-to-work order.
"I want to be very clear, Air Canada is choosing to do this to our passengers, to our company, because we are the face of the company, and they're trying to blame us for all this and getting together with their friends in the government to kind of circumvent all our rights," she said at a demonstration outside the Toronto airport.
She said workers are "done being abused and exploited."
"Where you have a multi-billion dollar company that's refusing to pay living wages to their employees, I just don't know."
CUPE originally announced its members were heading to the picket lines after being unable to reach an eleventh-hour deal with the airline, while Air Canada locked out its agents about 30 minutes later due to the strike action.
Air Canada had previously asked Hajdu to order the parties to enter a binding arbitration process.
CUPE said it is inviting Air Canada back to the table to negotiate a fair deal.
Flights on Air Canada Express, operated by Jazz or PAL, were not affected by the work stoppage.
Air Canada said it will offer people whose flights were cancelled options including a full refund, travel credit or rebooking on other carriers, though it noted that "capacity is currently limited due to the peak summer travel season."
-- With files from Natasha Baldin in Toronto and Morgan Lowrie in Montreal
This report by The Canadian Press was first published Aug. 17, 2025.
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Sarah Ritchie, The Canadian Press
