NEW YORK (AP) — Flight attendants with WestJet, Canada’s second-largest airline, went on strike Sunday in a dispute over pay.

The Canadian Union of Public Employees, which represents the 4,400 cabin crew at the airline, announced the strike on its Facebook page. WestJet confirmed the strike and canceled more than 300 flights as of early Sunday, snarling travel plans in Canada in the middle of a three-day weekend.

A key issue in the dispute was how flight attendants should be paid for duties performed while still on the ground. The union said some of that work is unpaid, while the company said its staff was indeed compensated, citing pay through a “credit hour” system rather than an hourly rate.

“We presented a proposal that would have set a new standard for cabin crew in Canada, making WestJet the only airline to offer an hourly rate covering all time before and after flights, plus a double-digit wage increase in year one among other priorities the union raised,” said Alexis von Hoensbroech, CEO of the WestJet Group. “Unfortunately, it wasn’t accepted.”

Alia Hussain, president of the union chapter that represents the cabin crew, said negotiators “tried until the very last minute to get a fair deal that recognizes the value of the work cabin crews do.”

“WestJet’s offer did not go far enough,” Hussain said.

Both sides said they were willing to resume negotiations to reach an agreement.

The airline said it could not operate any of its scheduled flights on Boeing 737s or 787s, and travelers will be refunded or reaccommodated. WestJet said it would contact people who reserved with them directly via email, while those who booked through a travel agent or third-party platform should reach out to them.

WestJet Encore flights operated on a Q400, as well as code-share flights operated by airline partners, remain unaffected.

Last summer, flight attendants at Air Canada, the country’s largest carrier, stranded more than 100,000 travelers during peak travel season with a strike partly over the same issue of groundwork. That work stoppage lasted three days before the sides came to an agreement.