Air Canada has applied to the Canada Industrial Relations Board for injunctive relief against its pilot union, CTV News has learned.

CTV's Ottawa Bureau Chief Robert Fife reported that 23 flights cancelled by the airline on Saturday were "due to pilots calling in sick," which also led to dozens of delays.

Half of the cancelled flights were out of Montreal, Fife said.

"Pilots Union refused to respond to AC's written requests to clarify it's not encouraging pilots to book off so AC went to CIRB," Fife tweeted late Saturday.

Fife noted Saturday night that Sunday will be an extremely busy travel day, as more families return from March break in Ontario, and travellers in British Columbia begin their holidays.

Earlier in the day, CTV News had confirmed that about a dozen pilots called in sick Saturday citing stress or fatigue as the reason for their absence.

Air Canada spokesperson Peter Fitzpatrick would only say the airline is facing "a number of operational challenges, including weather," during a peak travel weekend.

"However, the vast majority of Air Canada employees are working hard to get our customers to destination safely," Fitzpatrick said Saturday afternoon in an email to

Air Canada posted warnings on its website Saturday about potential fog-related delays in Montreal, Toronto, Ottawa, New York and Boston.

The airline also warned of possible flight disruptions in St. John's, Nfld. because of freezing rain and in Las Vegas due to strong winds.

The cancellations and delays come days after letters revealed that some Air Canada pilots had threatened to slow down company operations in response to Ottawa blocking potential strike action with back-to-work legislation.

A bulletin sent out Friday evening by Jean-Marc Belanger, chair of the Air Canada Pilots Association, indicated that he would also be calling in sick due to stress.

"Pilots, for public safety reasons can call in sick if they feel they're fatigued or tired," Fife noted earlier Saturday. "But they obviously can't call in if they're using it as part of a labour dispute or a work stoppage."

"Cancelled" notices lit up Air Canada flight boards just as thousands of Ontarians made their way home from their March Break vacations.

At Toronto's Pearson International Airport, the country's busiest travel hub, at least four flights from Montreal were delayed and two cancelled on Saturday afternoon.

Another flight, from Calgary to Toronto, was also cancelled, leaving would-be passenger and Liberal MP Jim Karygiannis stranded.

"We've got to come to a solution," Karygiannis. "Pilots can't just call in sick. The travelling public won't put up with it. A lot of people are frustrated and fed up."

Michael Levesque's flight from Las Vegas was cancelled Saturday, a move the airline told him was due to bad weather.

Levesque told CTV News that if "my flight doesn't take off tomorrow, I'm going to be a little more upset than I am right now."

Fife reported earlier Saturday afternoon that Air Canada had tried to get other pilots to come in to work.

Bill C-33, back-to-work legislation approved by the Senate on Thursday, ensures Air Canada's labour disputes will be sent to binding arbitration.

The bill covers disputes with two unions, one covering about 8,600 mechanics, baggage handlers and ground crew and the other covering about 3,000 pilots.

Airline management warned pilots this week that if they used sick days as part of a job action, they would face sanctions, including discharge.

Labour Minister Lisa Raitt said Saturday that if Air Canada believes the pilots were engaging in an illegal strike, "they can bring this matter to the Canada Industrial Relations Board."

With a report from CTV's Daniele Hamamdjian