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.

Air Canada has canceled most of its flights over the next few days to prepare for a strike by flight attendants. Some travelers may end up stranded as a result.

Air Canada said it will start cancelling flights on Thursday ahead of a possible strike by its flight attendants.