Where I'm from we sorted this out with laws. It's not hard to figure out if one of your workers are associating with a union, but you're not allowed to treat them differently based on that. Laws make sure you don't, even though you technically could.
The tricky part is proving you’re being treated differently and that’s the reason why. Trying to legislate human behavior at that level doesn’t seem to work well.
My company has rules against retaliation. Good luck proving that’s the reason you didn’t get promoted, or were left off of a project. People get left off projects and don’t get promoted all the time. Keeping your job because the company is legally obligated to sounds like an uncomfortable working environment.
