Unions are legal in all occupations.
One caveat: the legal protections of the right to unionize apply to non-supervisors. If you have people who report to you, your power to unionize is pretty limited.
There are also some specialized jobs that aren’t allowed to unionize by either federal or state law: actual soldiers in the Army, certain political jobs, etc.
But for the most part, if you are employed, you’re probably allowed to unionize (and protected against retaliation even in an unsuccessful union drive).
And just like that you’ve shown that gravity batteries aren’t feasible.
Storage is going to be a big part of the solution going forward. But it’s going to be chemical batteries and thermal batteries, not gravity batteries.