Earlier quoted context omitted.
Didn't California stop companies from preventing their ex-employees from working for competitors? Sounds like they're doing exactly what you want. https://en.wikipedia.org/wiki/Non-compete_clause#California
What does that have to do with unions?
Seems like you only want to prevent unions from doing this, but not employers. You also want to prevent them entering into contracts with employers. It's not really a consistent argument is it?