Extreme example: suppose a company has 100 employees. Four of them are in the union bargaining team and they just happen to all work for the widgets department because of an accident of history or randomness etc. The widgets department has 10 people overall.

Now the company decides for business reasons entirely unrelated to unions, that thanks to GPT they don't need so many people in the widgets department. So they fire 8 people from widgets. Assume further that they went out of their way to protect the union bargainers: of those 8 people fired, only 2 are in the union bargaining team. (That means that the remaining 2 widgets people are both union bargainers.)

Even though the company went out of their way to protect the union bargainers, statistically they only laid off 8% of the company, but 50% of union bargainers. Would that be illegal or even unfair?

(In the real world, I am fairly sure that union bargainers are concentrated in some departments. Mostly because it attracts certain kinds of people, and different departments also attract certain kinds of people.

But, of course, I have no clue what the reality inside of Bandcamp was like. I'm just speculating about hypothetical examples.)

Edit: also, another confounding factor that hasn't been discussed is job role/department. Layoffs and union membership are definitely not evenly distributed across role/department, but there is not enough info in the article to know if the layoffs were targeting specific roles or uniform across the company.