The Constitution doesnt really address anyone’s right to work. If you dont want to work for a Union, find a non-union job or move. No one is compelled into anything.
Not compelled? Really?
Do employers have a right to sign employees to a contract strictly forbidding union membership? Of course not. But the union bosses are allowed to extort contracts requiring union membership or, the distinction without a difference, a mandatory agency fee. That's wrong.
If you want to defend the "right" of employers to enter into such an agreement with a union, then you should also defend the right of employers to enter into strict non-union arrangements. Freedom of choice needs to run in both directions.