Legal Question in Employment Law in Illinois

Union rules, company policy, salary tracks, years of service and other factors can produce odd results sometimes. No, there's nothing inherently illegal about this, unless there is a protected class involved and there is discrimation that can be proven: race, gender.... It may be unwise from a management point of view, however, but I've seen very odd situations. Typically this happens in a company where times have changed and the company could no longer support the pay structure of its employees, so older employees were typically offered "early retirement" to get them off the payroll and a new crop of people are brought in under a new, and lower, pay structure. But if a few older employees hang on, they may be vested in their rights and until mandatory retirement, get to keep their compensation structure unless and until some other kind of event --- cause for termination, etc. If there's more to the story, however, feel free.