2 supervisors were told that our rate was lower due to our discipline but another sup of some discipline got the same as others. Is this legal

Discrimination generally occurs when one protected group is treated less favorably than another similarly situated group. Protections from discrimination range from age, disability, race, sex, and so on. Your question raises equal pay issues, but it's not clear if there's a disparity in pay because one protected group is being treated better or worse than another. The question also suggests all supervisors are being paid the same, so the likelihood of discrimination, or having case, is unlikely.