From the article:
In an FAQ on the union’s website, it’s explained that discussions of a union began after the layoffs at CD Projekt, which amounted to roughly 100 people. “This event created a tremendous amount of stress and insecurity, affecting our mental health and leading to the creation of this union in response,” reads the FAQ. "Having a union means having more security, transparency, better protection, and a stronger voice in times of crisis.
One issue is that unions have failed to globalize while industries have. CDPR could simply chose to bypass the union by opening a dev studio in a country with no or less union presence.
Given the recent wave of layoffs in the game industry, they’ll have no shortage finding capable people.