Why would you share your "not-union" membership with your employer? Instead, use it as a coordinator between your peers to prevent being underpaid and overworked do to information disparity you normally have in your relationship with you employer and if you get screwed it turns out you have access to lawyers.
Something of that sort.
To prevent this, you'd have to get your "not-Union" to either have huge solidarity, or lobby the government to make that a protected class.
Maybe if you went for the first you could make a song about it, how about "Solidarity not-for-finite-periods-of-time"?
It's why some companies will try to find ways to fire you if you share your salary.
Without the threat of collective action, the idea is toothless.
In the current situation, companies have access to this and employees don’t.
You’re going to negotiate with the knowledge in par with the company that is interested in having you.
Knowledge is power. - France is bacon.
Unless companies conspire not to hire you in order to depress wages.
https://variety.com/2017/biz/news/disney-settlement-wage-fix...
What problem with unions are you trying to solve here?
It’s owned by a trust or something similar.