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If you’re flying WestJet over Canada’s August long weekend, you may want to keep a close eye on your booking.

WestJet’s flight attendants have voted 99.4% in favor of strike action, meaning nearly 4,400 cabin crew members could legally walk off the job as early as August 2—just before one of the busiest travel weekends of the summer.

At the heart of the dispute is pay.

The union says flight attendants spend an average of 35 hours a month working unpaid while boarding passengers, helping during ground delays, and preparing the cabin before takeoff.

WestJet says its “credit hour” pay system compensates crews for all the work they perform and notes it’s a common model across North America.

The airline also says negotiations are continuing and that a strike is not inevitable.

Because either side must give 72 hours’ notice, travelers may not know whether flights will be affected until the end of July.

With summer vacations on the line, both the airline and the union say they still hope to reach a deal before any disruption happens.