It's not even in the same state, let alone the same ballpark, as illegal.
The only time you are guaranteed a raise under the law is if minimum wage is raised by the appropriate legislative body AND your current wage is below the new minimum. Beyond that, it's entirely up to the employer who gets a raise and who does not. As long as they are not making the decisions as to who does and who doesn't based on a characteristic protected by law (race, religion, disability etc.) they are perfectly free to give raises to some and not to all. What group you are assigned to, department you work for, or job description you work under, are NOT protected by law. They could put a list of employee names up on the wall, throw darts at it, and give raises to only the ones whose names are hit with darts and it would be perfectly legal.