Ok you are referring to the 14th amendment's "equal protection" law which requires that
government, including the state
governments, must treat all equally before the law. I think equal application of the law is just and necessary in a free society; I agree such treatment in application of the law is a right. However, it is a misconception that this applies to how citizens or employers must, by right, treat other citizens. I deny individuals have a right, enforced by government, to have all other individuals (and employers) treat them equally. I quickly add i) that I believe people have a moral obligation to treat others equitably, and ii) that I recognize nonetheless that there is substantial federal law in place that attempts to force the issue on matters of race, gender, sexual preference, disability; with another category added every ten years or so it seems.
The rules for non-government employers* came
not from the US Constitution but from the 1964 Civil Rights Act, specifically
http://en.wikipedia.org/wiki/Civil_Rights_Act_of_1964#Title_VII", sexual preference, and so on. Such
federal laws would not have been permissible under the constitution before the New Deal era SCOTUS decisions expanded the federal government's power.
*Government employers (public schools, etc) are subject to the equal protection clause as demonstrated by http://en.wikipedia.org/wiki/Brown_v._Board_of_Education" , etc.