I believe you are arguing I could always choose not to work. I wish to work for an employer and the employer wishes to work with me. In this hypothetical there is required membership with an unrelated party I do not wish to associate with.

If I wanted to go to a coffee shop and that shop wanted to serve me coffee but the mafia is standing outside saying I have to pay them before I can go in, they are in fact forcing me to pay or turn away.

The party’s not unrelated.

Yes, in both cases.

Are boards of directors unrelated parties you’re forced to associate with if you don’t want to severely limit your employment options?

The people the owners of the company have selected to run the company on their behalf are directly related to a company. I fail to see the similarity.

It’s a legally required body for many companies. It’s being imposed by law. Same as required unions would be.

I've never been forced to become a member of a corporate board. This proposal however is that I be required to join a union. That is the material difference.

True. You’re merely forced to be subject to their decisions, made on behalf of and in the interest of people who aren’t you.

[edit] I’m getting the sense that if we just restructure this so the union exists and does normal union stuff but you don’t have to “be a member” (but do have to abide by its decisions or else leave, as with a board) you’d be ok with it? Like it’s mainly a semantic problem?

I see it as more than a semantic problem, but the problem does boil down to the membership. If they are the lawful structure I'll abide by their decisions, I just don't want to be forced to join.

So it’s exactly the same as a union, in a situation where the union is the lawful structure of worker bodies in the country you’re working in.

I hate the idea. I've been in a union once and will never willingly do that again, but it would be more palatable if they couldn't claim me as a 'member'.