"Does this mean teacher unions too? So when there's a strike those who want to teach their students can do so without consequence?"
John Mortimer of Labourwatch was kind enough to provide this answer:
To answer Anonymous re teachers working during a strike. Your right to work could be constrained if the employer refuses to open the workplace and let you work. Not all employers during strikes are prepared to open up to non-managers. Usually it is because they fear union violence and most police forces have policies of not enforcing all aspects of the criminal code during a strike.
The "desk drawers" of lawyers and security firms are full of video of police watching as strikers perpetrate violence, particularly to property. I have been advised that police actually swear oaths to uphold the law, not to keep the peace. In one province a sharp group of people have been assessing what to do about going after governments and the police that refuse to enforce and ensure the rule of law including whether or not these parties can be successfully sued.
Finally, Saskatchewan has Canada's only statute forcing union membership on almost all unionized workers. It also has Canada's only statute law (thank you "Conservative Premier Grant Devine") giving unions the right to fine union members (cannot fine the few who are able to avoid forced membership) who cross a picket line to do their jobs. A statute like this trumps the common law principle that protected the PSAC members - courts do not enforce penalties between private parties to a contract.