It's bad optics (and I personally think the company can piss off), but I don't think they technically broke the letter of the law. Colorado doesn't have good faith exemptions to at-will so as long as it wasn't a protected class thing, I think they can do whatever they want, AFAICT

*edit: I guess discussing wages is protected(?) (https://www.jacksonlewis.com/resources-publication/colorado-...) - but they didn't pick the reason, so I guess it boils down to how good lawyers are