Toronto Air Canada said it expects to resume normal operations after a labour board declared a strike by pilots at the country's biggest airline as illegal.
The Canada Industrial Relations Board ordered the Air Canada Pilots Association (ACPA) "to take all reasonable steps to bring to an end the illegal strike" and to require all participating pilots to "immediately return to work", the carrier said late on Friday.
Air Canada cancelled about 75 flights on Friday because of an "illegal job action" by some of its pilots, the airline said in a statement.
Air Canada's dispute involves two of its key unions, including the one representing its 3,000 pilots.
Earlier last week it said in a letter to the pilots' union that a number of pilots had planned to book off sick on Friday, although they were fit to fly.
ACPA president Paul Strachan said the union will comply with any labour board decision. But he warned that pilots are fed up. "We all need to be very cognizant of the real risk that, at some point, the pilots will feel so beaten down and so helpless that they're going to lash back and not even this organisation is going to be able to control the outcome of events," he said.
"I think we have the ear of most of them, still the vast majority of them. But I think there's a growing frustration among them that it's a hopeless situation, they feel like cattle being herded into the killing yards."
Montreal-based Air Canada cancelled 36 of 690 flights scheduled to depart from its hub at Toronto's Pearson International Airport, according to the airport's website, with a possible snowball effect on flights from other centres.
Air Canada wants to set up a discount airline to help its bottom line at a difficult time for the aviation sector. Its unions oppose the plan, fearing that their benefits and job security could be at risk.
The Canadian parliament passed a law last month that sent separate disputes with the Air Canada pilots and with its machinists to binding arbitration. That prevents the machinists from striking, and the airline from locking out the pilots.
"It is our duty to advise all pilots that ACPA's right to strike and Air Canada's right to lock out its employees are suspended until a new collective agreement takes effect," the pilots union told its members last week.
Noting that it has filed a motion in court to quash the legislation, the union added: "Until the law is struck down, we must all comply with it."
Air Canada's director of flying operations said in a letter to the pilots that the company would not tolerate pilots abusing the rules about "fitness to fly".
George Smith, a Queen's University labour relations expert and former Air Canada executive, said he saw no chance of a positive outcome to the dispute.
"You're going to continue to annoy customers, no doubt there will be a legal response to this, and once again the pilots will be challenged for conducting an illegal strike. The government will say they're not going to tolerate it and ratchet it up again, making it worse, rather than better."
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 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 flights.
Canada's labour minister Lisa Raitt encouraged the two sides to resolve their disputes and restore passenger confidence.
Air Canada said it would allow customers booked on flights today and tomorrow to book alternate travel without penalty.
Shares of Air Canada closed unchanged at C$0.86 Friday.