Porter posted a list of cancelled flights for Tuesday and Wednesday on its website. So far 41 flights have been cancelled for Tuesday and four are cancelled for Wednesday morning.
Officials at Porter told CBC News that the cancellations are due to outages affecting their system provider, Navitaire, which manages bookings for several small low-budget airlines. Navitaire is used by about 50 flight companies around the world, several of which are also experiencing problems.
Air Canada does not use the Navitaire system and is operating normally.
It is unclear when the system will be restored. Porter is advising passengers to call 1-888-619-8622 later Tuesday night and Wednesday morning to find out the status of their flights.
Meanwhile, at Billy Bishop Airport, passengers were left stranded.
Patrick Cooper, who was headed to Montreal for a hockey game, arrived at the airport only to be told that his flight was cancelled.
"There were people everywhere, sitting everywhere, waiting for their flights," he told CBC News.
Another passenger, Kaitlyn McCave, was scheduled for a flight to Windsor, where she lives. At first she was told her flight was delayed, but later found out that it was cancelled. She was at the airport for four hours. "I could have driven home by now," she said.