It is illegal to discriminate against someone on the basis of a particular characteristic only if that characteristic is listed in a federal, state, or local law prohibiting discrimination.
Federal laws. Federal law prohibits discrimination on the basis of race, gender, pregnancy, national origin (including affiliation with a Native American tribe), religion, disability, citizenship status, genetic information, and age (if the person is at least 40 years old). To learn more about the federal antidiscrimination laws, see Nolo's article Federal Antidiscrimination Laws.
State and local laws. State and local laws often prohibit additional types of discrimination, including discrimination on the basis of marriage, sexual orientation, and weight. (Almost half of the states prohibit private employers from making employment decisions based on sexual orientation, as do many county and municipal governments. For more information, see Nolo's article Preventing Sexual Orientation Discrimination in the Workplace.) To learn more about your state and local laws, contact your state fair employment office.