The Canada Industrial Relations Board ordered airline staff back to work by 2 p.m. Sunday after the government intervened and Air Canada said it planned to resume flights Sunday evening.

Canada’s largest airline now says it will resume flights Monday evening. Air Canada said in a statement that the union “illegally directed its flight attendant members to defy a direction from the Canadian Industrial Relations Board.”

“Our members are not going back to work,” Canadian Union of Public Employees national president Mark Hancock said outside Toronto’s Pearson International 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 were picketing Sunday morning. He said they won’t return Tuesday either.

Flight attendants chanted “Don’t blame me, blame AC” outside Pearson.

The federal government didn’t immediately provide comment on the union refusing to return to work.

Hancock said the “whole process has been unfair” and said the union will challenge what it called an unconstitutional order.

Less than 12 hours after workers walked off the job, Federal Jobs Minister Patty Hajdu ordered the 10,000 flight attendants back to work, saying now is not the time to take risks with the economy and noting the unprecedented tariffs the U.S. has imposed on Canada. Hajdu referred the work stoppage to the Canada Industrial Relations Board.

The airline said the CIRB has extended the term of the existing collective agreement until a new one is determined by the arbitrator.

The shutdown of Canada’s largest airline early Saturday was impacting about 130,000 people a day. Air Canada operates around 700 flights per day.

Tourist Mel Durston from southern England was trying to make the most of sightseeing in Canada. But she said she doesn’t have a way to continue her journey.

“We wanted to go see the Rockies, but we might not get there because of this,” Durston said. “We might have to head straight back.”

James Hart and Zahara Virani were visiting Toronto from Calgary, Alberta for what they thought would be a fun weekend. But they ended up paying $2,600 Canadian ($1,880) to fly with another airline on a later day after their Air Canada flight got canceled.

“It’s a little frustrating and stressful, but at the same time, I don’t blame the flight attendants at all,” Virani said. “What they’re asking for is not unreasonable whatsoever.”

Flight attendants walked off the job around 1 a.m. EDT on Saturday. Around the same time, Air Canada said it would begin locking flight attendants out of airports.

The bitter contract fight escalated Friday as the union turned down Air Canada’s prior request to enter into government-directed arbitration, which allows a third-party mediator to decide the terms of a new contract.

Last year, the government forced the country’s two major railroads into arbitration with their labor union during a work stoppage. The union for the rail workers is suing, arguing the government is removing a union’s leverage in negotiations.

Hajdu maintained that her Liberal government is not anti-union, saying it is clear the two sides are at an impasse.

Passengers whose flights are impacted will be eligible to request a full refund on the airline’s website or mobile app, according to Air Canada.

The airline said it would also offer alternative travel options through other Canadian and foreign airlines when possible. Still, it warned that it could not guarantee immediate rebooking because flights on other airlines are already full “due to the summer travel peak.”

Air Canada and CUPE have been in contract talks for about eight months, but they have yet to reach a tentative deal. Both sides have said they remain far apart on the issue of pay and the unpaid work flight attendants do when planes aren’t in the air.

The airline’s latest offer included a 38% increase in total compensation, including benefits and pensions, over four years, that it said “would have made our flight attendants the best compensated in Canada.”

But the union pushed back, saying the proposed 8% raise in the first year didn’t go far enough because of inflation.