Aug 2 (Reuters) - Flight attendants at Canada's WestJet went on strike on Sunday ‌after failing to reach a deal with the country's second-largest carrier, grounding flights during the busy summer travel season.

The Canadian Union of Public Employees, which represents 4,400 flight attendants at the carrier, majority-owned by Onex Corp (ONEX.TO), opens new tab, is seeking pay ​for its members from the time they check in until they clock out, which is ​not currently the case.

The strike follows a four-day work stoppage by flight attendants last August ⁠at larger rival Air Canada (AC.TO), opens new tab, highlighting broader efforts by flight attendants in Canada and the U.S. ​to challenge a compensation structure that mostly pays cabin crew when an aircraft is in motion.

The union ​had given 72 hours' notice on Thursday to the airline signaling that a strike could come if talks failed to produce an agreement, following which WestJet issued a lock-out notice.

The union on Sunday said it had tried until the last minute ​to reach a deal but that “WestJet's offer did not go far enough.”

"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.

The airline, which has a domestic market share of about 30%, confirmed the work stoppage and said it would refund or reaccommodate affected passengers.

"We presented a proposal... 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. Unfortunately, it ​wasn't accepted," WestJet CEO ⁠Alexis von Hoensbroech said.

Patty Hajdu, Canada's jobs minister, described the development as 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 ⁠added.

The airline canceled 309 flights through Sunday night in anticipation of the strike. It did so to "minimize the risk of stranding guests and aircraft."

The Canadian government intervened to stop the Air Canada strike last year, which was ⁠later defied ​by flight attendants. The union's WestJet division said it hoped ​the Canadian government would not interfere in the bargaining process.