WestJet flight attendants began a strike on Sunday after last-minute talks collapsed. The stoppage cancelled hundreds of flights, disrupted holiday travel and sharpened the pay dispute over unpaid work.

Flight attendants at Canada’s WestJet went on strike on Sunday after talks fell through with the country’s second-largest carrier, grounding flights during the busy summer season and adding to challenges by cabin crews across North America to the industry’s pay structure.

Approximately 250,000 travellers, according to the airline, have had their flights cancelled on a three-day holiday weekend in Canada, and more passengers will be affected depending on how long the work stoppage lasts.

The carrier, which has a domestic market share of 30% and flies to destinations in the US, the Caribbean, Central America and Europe, had cancelled 615 flights as of mid-morning Sunday, according to aviation analytics company Cirium. WestJet is majority-owned by Onex Corp ONEX.TO.

The Canadian Union of Public Employees, which represents 4,400 flight attendants at the carrier, is seeking pay for its members from the time they check in until they clock out, instead of mostly just for time when their aircraft is in motion.

Flight attendants staged a four-day work stoppage last August at larger rival Air Canada AC.TO in a similar challenge to airlines’ compensation structure.

The union had given 72 hours’ notice on Thursday to WestJet, signaling that a strike could occur if talks failed to produce an agreement. WestJet subsequently issued a lockout notice.

Both sides said they tried until the last minute to reach a deal but were unsuccessful.

“We are on strike because we believe we deserve better. We are ready to go back to the table to settle,” said Alia Hussain, president of the union’s WestJet component.

On Sunday, WestJet released details of the deal it said it had offered the union in an effort to avert a strike, including a 13% wage increase this year followed by 2.5% wage increases each year through 2029.

WestJet also said it offered additional pay for all hours worked, equivalent to another 12% salary increase. The company said the premium was offered to address the union’s complaints regarding unpaid work.

A union representative did not immediately respond to a Reuters request for comment on the airline’s proposal.

WestJet said on Sunday it would refund or reaccommodate affected passengers, although some travelers posting on social media reported difficulties reaching the airline’s customer service department and confusion about what to do next.

Patty Hajdu, Canada’s jobs minister, said the latest developments in the dispute at the carrier were disappointing.

“A strike or lockout does not mean an agreement can’t be reached; the expectation is that parties can and should come to an agreement at the bargaining table,” she said.

The Canadian government intervened to stop the Air Canada strike last year, but flight attendants eventually defied that effort. The union’s WestJet division said it hoped the Canadian government would not interfere in the bargaining process.