The carrier is in dispute with two of its key unions, including the one representing its 3,000 pilots. It urged customers to check the status of their flights before leaving for the airport.

"Due to illegal job action by some Air Canada pilots, Air Canada is experiencing delays and some cancellations of flights today," it said in a statement. "Air Canada is making every effort to re-accommodate affected customers on alternate flights."

A spokesman said Air Canada (ACb.TO) typically has around 1,500 flights a day. About 660 of those flights are on the mainline carrier, with the remainder on its regional carrier.

The pilots union was not immediately available for comment. It had previously told its pilots in a letter that it has not and will not condone illegal actions from its pilots.

It said a letter from Air Canada's director of flying operations alleged that pilots would book off sick on Friday under an illegal work disruption, when they were fit to fly.

This is the second time in a matter of weeks that the airline has cancelled and delayed flights amid reports of a pilot sick-out. Delays on the previous occasion were also attributed to fog and to a fire on a runway at the main Toronto airport.

Air Canada was also hit by a wildcat strike last month, when ground crew workers walked off the job, disrupting dozens of Air Canada flights from Toronto and Montreal.

Earlier in March, the Canadian government enacted a law sending separate Air Canada disputes with machinists and pilots to binding arbitration. That prevents the machinists from striking, and the airline from locking out the pilots.

Both unions are fighting that law in court.

Canada's Labor Minister Lisa Raitt on Friday encouraged the parties to resolve their disputes and restore passenger confidence.

"By introducing and passing back to work legislation, we put the public interest and the Canadian economy first to ensure that Canadians can continue to fly," Raitt said in a statement.

"The Act provides a process to the parties to achieve a binding collective agreement and encourage them to follow the process."

(Reporting by Euan Rocha and Susan Taylor; Editing by Janet Guttsman)

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