WestJet announced on Saturday evening that a system-wide outage is causing a "number of delays," and has led to one cancelled flight.
“We are actively working to get systems back up and running and anticipate service will be restored shortly,” the airline said on its Twitter account.
Many WestJet passengers appear to have been waiting for hours to board planes, with some missing connections, according to several social media posts on Twitter.
One passenger said she was on "hour five" of waiting at Calgary International Airport.
Calgary International Airport, calling it a "global IT outage" has also warned passengers flying through YYC about potential delays, as did Vancouver International Airport.
WestJet also experienced a system outage in July due to a train derailment, which led to delayed WestJet flights in Canada and abroad.
There have been no recent updates as to when the outage will be resolved.