Aug. 2 (UPI) — Hundreds of flights were canceled in Canada on Sunday after flight attendants at the country’s second-largest airline, WestJet, went on strike.

Some 4,400 cabin crew at the airline have been in heated negotiations with the airline over how they should be paid while aircraft is still on the ground.

WestJet said the strike affects some 250,000 guests booked to fly over the three-day weekend, one of Canada’s busiest travel times during the year.

“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,” the airline said in a statement.

“Unfortunately, it wasn’t accepted.”

Alia Hussain, president of the Canadian Union of Public Employees, said the union that represents cabin crews was unable to reach an acceptable agreement with WestJet after 11 months of bargaining.

“We tried until the very last minute to get a fair deal that recognizes the value of the work cabin crews do,” Hussain said in a statement. “WestJet’s offer did not go far enough.”

WestJet said it is offering refunds or re-accommodations for customers affected. Those booking directly through the airline will receive emails with next steps, while customers who went through third-party agencies should reach out to them.