Overtime pay withheld due to company policy
I was told that there was no overtime at my job. There is an annual event that we all go to and get paid OT for but that's it. My Managers were aware that I was working later on a big project I was given and I was not paid for it. A year later, I questioned why we are made to sign pre-filled with 40 hours "timecards" if we (all hourly employees) paid a straight 40 hours and it was mentioned that overtime had to be pre-approved, a policy I never heard of. I then asked if anyone was getting overtime and through various measures between my boss and I, where he showed me payroll data and I showed him payroll data, that I had access to (pulled-up in his presence) revealing that a manager - who was aware of my own OT, & processes payroll, was paid for OT, while I was not.
I did not demand payment, just advised my superior that it was an unethical practice to pay selective OT.
I have since been threatened with legal action by the manager who paid OT to themselves and berated by coworkers who were told a skewed count of what transpired during that confidential conversation with my manager. Since, a memorandum has been circulated stating immediate termination will occur if anyone is"illegally" accessing employee payroll records.
My question is: Can they fire me or take legal action against me?
I'm aware I have a case but would prefer to keep my job than take it there.