If you have a flight booked with Westjet or Swoop, you might want to re-think the trip.

Hundreds of pilots have given 72-hour strike notice, and that means they could hit the picket lines just before the long weekend.

“After nine months of negotiating, management still fails to understand current labour market conditions, leading to a mass exodus of our pilots in search of better work opportunities, and more will follow if this agreement does not meet our pilots’ needs,” said Captain Bernard Lewall, chair of the WestJet ALPA Master Executive Council (MEC). “Without the economic and job security improvements our pilots require, WestJet will be parking planes, as they will not have enough pilots to operate them or accomplish its own growth strategy.”

As of 3:00 a.m. ET on May 19, the WestJet pilots plan to begin lawful job action, which could include grounding all aircraft and effectively shutting down operations.

The airline has responded by threatening to lock-out its pilots if a deal is not reached. Westjet is already preparing for the worst case scenario, and will offer flexible change and cancel options if you’re having second thoughts.

Both sides have been negotiating since September.

The issues in the dispute include pay, scheduling, and job security.