I’ll take a stab at this based on what I’ve learned from other threads (but mods, please let me know if I’ve got the legal details wrong). Technically this is ‘discrimination’ because one employee is being treated differently than another- but that’s only illegal if it’s based on the employee’s membership in a protected class (being female, being a certain race, etc). I don’t think having a history of mental illness counts as any protected class. It also doesn’t seem to run afoul of any ADA issues as the employee isn’t being denied a reasonable accommodation or anything. Maaaaybe it could be harassment, if anything? But I’m not seeing a genuine legal issue here, just a workplace quality of life matter.