In a private company, suits about being treated poorly for "retaliation" doesn't apply to most things. In other words, if those in power want to change the rules simply because they want to get rid of you, they can do it, legally. There's no "whistleblower" sort of protection for you in this very personal issue between you and the one manager which has caused him/her to dislike you and want to get rid of you.
If the company wants to, they do not even have to follow their own personnel policies. It sounds like the manager over you did something that wouldn't have been a big deal if you hadn't made one of it, and now they are mad at you, and they want you not to come back, so they are changing the rules so they can get you out without your qualifying for unemployment, which is pretty much your only recourse.