US Companies? It depends on the context: how damaging would a strike be, and how much of the important people can you get to join?
In the context of pro gaming, I have serious doubts that any union is viable outside games with a franchise model. There are just too many hungry people and too few spots at the top to ever have a meaningful strike.
Even with a franchise, the result of a Union forming may just be the dissolving of the franchise model (or the failure of the game as an esport) rather than the Union achieving political power.
