Canada’s biggest airline is poised to start canceling several dozen flights Thursday ahead of a weekend lockout of flight attendants that threatens to throw travel plans for tens of thousands into chaos during the peak summer season.

The dominant air carrier in Canada set in motion a process that could ground 130,000 passengers a day by Saturday.

Air Canada said it would reach out via email or text to let customers know if their flights are canceled. The cancellations on Thursday included some long-haul overseas flights. By the end of Friday, the airline expects to cancel 500 flights.