A lot of the reasons unions form in the USA are mitigated by Canadian labour laws. So you generally only see them in large work forces such as government employees, school teachers, and trades. People already get severance pay based on length of employment for getting fired without cause. If you’re laid off you can get EI (60% wages from gov’t).

So to answer your question… nothing probably -though I am speculating. Unless they did something egregious they likely broke no laws.