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 union representing 10,000 flight attendants for Canada's largest airline issued a 72-hour strike notice on Wednesday.

Air Canada said on Thursday it expects to cancel several dozen flights by day's end and around 500 flights by the end of Friday affecting 100,0000 passengers, ahead of a planned Saturday strike by its unionized flight attendants.