Employers can most definitely say they fired you and give a reason. They can in NC, anyway.
NC being a fire-at-will state might have something to do with it though. On every application I fill out there's questions about if you've been fired, what it was for, and the employer's phone number so they can call and ask if what they said matched your story.
If I thought I was working hard enough and I got fired I'd be monumentally pissed off as well. It sucks hardcore that there's nothing you can do about it though, legally or socially.