Race, color, religion, national origin, age, sex, pregnancy, citizenship, family, disability, veteran, genetics.
Technically speaking discrimination is not illegal. Only discrimination along certain axes, such as those listed above, is. States may have additional protected groups on top of that list.
If an employer wanted to pay veterans $1/hour more than non-veterans doing identical work, would that be allowed?
I believe that protected classes in the US aren't identifying things such as, "You can't discriminate against a woman". Rather, what they say is, "You can't discriminate based on anything related to gender". There may be some exceptions, like veterans as mentioned above, but they would be the exception.
Oh, okay... So affirmative-action programs to empower women and other groups are not discriminating against men due to their gender? Interesting double-standard they have there.
It's actual quite hypocritical, if you think about it. Putting a double-standard in place to fix a previous double-standard. But, I suppose, with the "power" of the state, most people think they can play social-architect and fix all the world's ills...from their armchair. Standards being only one "weapon" in their arsenal.