Air Canada was offering little explanation on why numerous flights, mostly originating from Montreal's Trudeau International Airport were cancelled or delayed on Saturday.
Websites for both the airline and the airport listed a number of delays and cancellations for flights between Montreal and other cities, including Toronto, Halifax, Saint John and some American destinations. Airports in Toronto and Vancouver were reporting a small number of cancellations or delays, but it wasn't clear if they were connected.
CTV News reported the disruptions are due to the fact that a dozen pilots called in sick because of stress or fatigue.
But Air Canada would not confirm the reason for the flight disruptions.
"On this peak travel weekend, we face a number of operational challenges, including weather, spokesman Peter Fitzpatrick said in an e-mail to The Canadian Press.
"The vast majority of Air Canada employees are working hard to get our customers to destination safely."
The disruptions come in the midst of a bitter feud between the airline and its pilots that prompted the federal government to step in earlier this month.
In the face of a threatened lockout by pilots and a strike by ground crew, the federal government referred the matter to the Canada Industrial Relations Board and also passed back-to-work legislation this week that referred the disputes to arbitration.
The union representing the pilots did not immediately comment.
Air Canada has been plagued with labour troubles all year. The federal government has had to intervene in contract disputes involving the airline's flight attendants and its customer service agents.