In theory it’s exceptionally illegal to curtail unionization efforts.

In practice, the law has been whittled away by decades of conservative judiciary decisions and weak department of labor enforcement. This isn’t helped at all by the balance of power.

Companies can afford to scare off some degree of workers, especially at the lower end of the salary range. Big businesses can survive shutting down a store or losing business at locations indefinitely. Big businesses can afford expensive lawyers and to indefinitely stay in litigation over union busting efforts.

For workers, it’s a completely different proposition. Is Walmart or Home Depot or Starbucks going to want to hire someone that is actively suing another major corporation for anything at all? It’s even worse if it’s labor rights related, but just suing them in the first place is going to make it a struggle to find employment at a lot of places. That’s even pretending they can find & afford lawyers. Or that they can handle the transition period from job A to job B even if it isn’t difficult to find job B.

These businesses hold all the cards and they know it. You see similar thinking, though different details, behind Hollywood’s decision to just try and wait out the striking writers and actors. They can survive losing billions of dollars in income a year from now with unmade projects; striking workers will struggle to get by with no salary.