The Fair Housing Act of 1968 (codified at 42 U.S.C. 3601-3619M) Title VIII of the Civil Rights Act of 1968 is a federal law protecting home buyers and renters from discrimination, as defined by protected classes including race, color, religion, age, sex, pregnancy, citizenship, sexual orientation, and more. There might also be additional state and local laws that provide even broader coverage than the federal law.
As a home seller, you have the obligation under the law to not discriminate on the basis of race, color, religion, sex, national origin, sexual orientation or handicap in marketing or selling your house. For those looking for more detailed information, please review the plain english version of the Fair Housing Act composed by the US Department of Housing and Urban Development ("HUD").
If you suspect unlawful discrimination in violation of the federal statute, or you believe you are a victim of housing discrimination, you can file a housing complaint directly to the Office of Fair Housing and Equal Opportunity ("FHEO") and the HUD online.