I flatly reject the notion that, with as massive a power differential as the employer-employee relationship structurally entails, it qualifies as an "exercise" of some "natural right of association".

With the way we've chosen to run our world, such that there are orders of magnitude fewer people offering jobs than there are needing them, one side of that dynamic has tremendous power to dictate terms to the other. That is not remotely an equitable relationship, and to suggest that participating in it is some sort of "exercise" of a "natural right", that is freely entered into, is fatuously specious.