VANCOUVER, British Columbia (AP) — Flight attendants at WestJet, Canada’s second-largest airline, threatened Thursday to go on strike over unpaid work, a move that could disrupt travel during the busy summer season.

The union representing 4,400 cabin crew at WestJet issued a 72-hour strike notice.

That means that if an agreement isn’t reached, the strike could begin Sunday — at a time when the Monday, August 3 holiday in Canada creates a three-day weekend for many people.