Air Canada's flight attendants union went on strike last summer when contract negotiations weren't working, and West Jet's flight attendants union didn't start contract negotiations until later in the year.

If they did, the government would step in and decide for all parties what the terms of the contracts will be.

A lot of bad things would happen if there were zero airlines in operation. Just as collusion between companies is bad, collusion between unions is bad. There's a difference between taking action that negatively impacts a company and taking action that negatively impacts a whole country. So the government would need to be directly involved.