A work stoppage looms for 4,400 flight attendants at Canada's second-largest air carrier after their union issued a 72-hour strike notice early Thursday morning. WestJet responded to the union's move by issuing a 72-hour lockout notice. For summer travellers worried about what this means for their plans, here's what you need to know.

The clock is ticking down toward a strike deadline that could see 4,400 WestJet flight attendants hit the picket line as soon as Sunday.

The Canadian Union of Public Employees Local 8125 gave the airline notice early Thursday morning, the union said in a post on its website.