Flight attendants at WestJet, Canada's second-largest airline, went on strike on Sunday after the sides failed to reach an agreement on pay terms, the Associated Press reports.

Amid the labor action, the carrier has already canceled more than 300 flights, disrupting the plans of thousands of passengers during the long holiday weekend.

The Canadian Union of Public Employees (CUPE), which represents about 4,400 cabin crew members, announced the start of the strike. The airline itself confirmed the labor action and said it would be unable to operate scheduled flights on Boeing 737 and Boeing 787 aircraft.

The main point of contention was pay for flight attendants' work before departure and after landing. The union argues that some duties performed on the ground effectively remain unpaid. WestJet insists that employees are compensated under a so-called "credit hours" system rather than hourly pay.

WestJet Group CEO Alexis von Hoensbroech said the company had offered to switch to hourly pay for all working time before and after flights, as well as to significantly raise wages in the first year of the new agreement. However, according to him, the union rejected the proposal.

For her part, Aliya Hussain, head of the flight attendants' union, said negotiators had tried "until the very last minute" to secure a fair agreement, but the airline's offer proved insufficient.

Both sides said they were ready to resume negotiations.

WestJet said passengers on canceled flights would be able to request refunds or rebook their tickets. At the same time, WestJet Encore regional flights on Q400 aircraft, as well as codeshare flights operated by partner airlines, continue to run as normal.

The dispute over pay for flight attendants' ground working time has previously caused major disruptions to air travel in Canada. Last summer, a similar three-day strike by Air Canada employees affected more than 100,000 passengers and ended after a compromise agreement was reached.