* WestJet cancelled 309 flights through Sunday night before

the strike began

* Union seeks pay from check-in until members clock out

* WestJet says it will refund or reaccommodate affected

passengers

By Sumedha Mukherjee and Shubham Kalia

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 (CUPE), which represents

4,400 flight attendants at the carrier, majority-owned by Onex

Corp ( ONEXF ), 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 ( ACDVF ), 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.

CUPE 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 WestJet component of the CUPE.

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.

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 ( ACDVF ) 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.