I worked for a company that had an off duty conduct policy. It was intended, I think, for people who get arrested or convicted for things that happen while they are not at work, eg drunk driving. However (comma pause for effect) it was generally used against people who complained about their boss or work on their own time. Kind of like this.
That company is IPC International Corporation. It's a contract security firm, so I doubt many people here would work for them, but throwing it out there just in case. It wasn't the way I would have liked to leave, but I thank G-d every day that I never have to deal with them again. It may seem like I have a lot of resentment toward them. Maybe I do... hindsight being 20/20 I should have taken unemployment and finished my degree. (which I am doing now.)
Also that policy applied to the guards, maybe not management. Or it may be even more restrictive for management.