The union representing pilots said Tuesday that it filed suit in Ontario Superior Court, while the International Association of Machinists and Aerospace Workers (IAMAW) added it will soon pursue its own effort.
Both groups, which together represent more than 11,000 airline employees, are the last group of workers without updated collective agreements.
The pilots said the law passed last week forces them to fly and accept a contract imposed by arbitration in contravention of the Canadian Charter of Rights and Freedoms.
"The legislation was Draconian overkill," Capt. Paul Strachan, president of the Air Canada Pilots Associations said in an interview.
Neither side was able to strike or lock out workers once Labour Minister Lisa Raitt referred the matter to the Canada Industrial Relations Board.
The pilots said the Protecting Air Service Act prohibits pilots from exercising their right to strike and contravenes three sections of the Charter.
"We believe there's jurisprudence to support our position and we'll take it as far as we have to."
Raitt wouldn't comment specifically on the pilots lawsuit, but said the government acted to prevent a work stoppage that would have a significant effect on the economy.
"It was in the public interest that we passed legislation to prevent both a strike and lock out," she said in an email.
In an application before the Ontario court, the pilots also argue that forcing them to fly conflicts with their legal obligations under the Canadian Aviation Regulations. Those regulations prohibit pilots from flying if they have any reason to believe they are unfit to properly perform their duties.
Several Air Canada (TSX:AC.B) flights were cancelled last weekend when pilots called in sick after they determined through self-assessments that they were unfit to fly.
Strachan insisted that the union didn't orchestrate pilots to call in sick. Air Canada has asked the Canada Industrial Labour Relations Board to declare the actions an illegal strike.
The airline declined to comment on the legal challenge by pilots because it was before the courts. It said the rules governing aviation are in place to protect pilots who are not fit to fly.
"While Air Canada supports the right of its employees to book off when they are unwell or otherwise incapacitated, we cannot condone such activities being used as part of industrial action," airline spokeswoman Isabelle Arthur said in an email.
The CIRB will assess the airline's complaint after receiving written submissions due by next week.
"The members of ACPA have been under a significant amount of stress as a result of the unwillingness of Air Canada to negotiate a fair collective agreement, combined with the Minister of Labour's and Parliament's removal of their only means of engaging in meaningful collective bargaining," said the court filing.
The union said pilots have a "moral, legal and ethical responsibility" to assess their own fitness for duty.
"I can't hold a gun to our members' heads and say: 'Fly or else.' I won't do it," Strachan added.
"C-33 is incongruous with the Aeronautics Act and I can't climb inside of somebody's head and figure out how well they slept last night or what they've got on their minds."
The filing by Jean-Marc Belanger, chairman of ACPA's Master Executive Council, says the legislation tries to override that responsibility and compel pilots to fly by threatening them with fines of up to $1,000 if they don't report for duty. Union officials can be fined up to $50,000 per day.
"This is not only a legal issue, but also a public safety issue that should concern all passengers," Strachan said.
The pilots say the legislation's requirement for binding, final-offer arbitration is designed to favour the airline's position.
Such arbitration is usually only pursued when a limited number of issues remain unresolved, he added. The model was used, for example, to resolve Air Canada pension issues with customer service workers last year.
A better approach would have been to allow a seasoned arbitrator to carve out an agreement based on an evaluation of the merits of the proposals, Strachan said.
"One party is going to feel defeated no matter what and it may well work against the interests of the other party, the one who is ostensibly the victor."