June 26 (Reuters) - Canada's WestJet Airlines has begun

cancelling flights again after a union representing its

maintenance engineers rejected a new pay offer and served a

second strike notice, the carrier said on Wednesday.

WestJet said this action would lead to an estimated 25

flight cancellations from June 27-28 and impact over 3,300

travellers. The airline had earlier in the day said that the

work stoppage could occur as soon as June 28.

It is not clear how long the strike could go on for.

WestJet, which is backed by Onex Corp ( ONEXF ) and competes

with Air Canada ( ACDVF ), has been facing demands from employees

for better working conditions and higher salaries.

WestJet said it presented the Aircraft Mechanics Fraternal

Association (AMFA) with a "Canadian industry-leading agreement,"

which was better than the previous agreement that was rejected

by the union earlier in the day.

The offer that was rejected had presented aircraft

maintenance engineers with a 22% pay increase over four years.

AMFA did not immediately respond to a request for comment.

"It is especially devastating that the strike notice we have

received from AMFA forces us to begin cancelling flights and

parking aircraft, for the second time in just over a week," said

Diederik Pen, president of WestJet Airlines and group chief

operating officer.

The Calgary-based airline last week canceled 40 flights that

affected 6,500 customers after it was sent a 72-hour strike

notice by the union. The union withdrew the strike notice on

June 20 and agreed to return to discussions.

(Reporting by Rishabh Jaiswal in Bengaluru; Editing by Janane

Venkatraman and Sonia Cheema

)