Three Facebook users have sued the social networking giant over alleged discriminatory policies that they say violate the US Federal Housing Act of 1964.

Late last month, ProPublica published a story outlining the fact that Facebook’s advertising mechanism allowed for housing ads to exclude a specific “Ethnic Affinity,” such as “African-American” or “Asian-American.” ProPublica managed to post an ad placed in Facebook’s housing categories that excluded anyone with an “affinity” for African-American, Asian-American, or Hispanic people. When the ProPublica reporters showed the ad to prominent civil rights lawyer John Relman, he described it as "horrifying" and "as blatant a violation of the federal Fair Housing Act as one can find."

According to the proposed class-action lawsuit, by allowing such ads on its site, Facebook is in violation of the landmark civil rights legislation, which specifically prohibits housing advertisements to discriminate based on race, gender, color, religion, and other factors.

"This lawsuit does not seek to end Facebook’s Ad Platform, nor even to get rid of the "Exclude People" mechanism. There are legal, desirable uses for such functionalities. Plaintiffs seek to end only the illegal proscribed uses of these functions," the lawyers wrote in the civil complaint, which was filed last Friday.

The proposed class, if approved by a federal judge in San Francisco, would include any Facebook user in the United States who has “not seen an employment- or housing-related advertisement on Facebook within the last two years because the ad’s buyer used the Ad Platform’s ‘Exclude People’ functionality to exclude the class member based on race, color, religion, sex, familial status, or national origin.”

Genevieve Grdina, a Facebook spokeswoman, sent Ars a statement saying that the allegations were baseless. “The lawsuit is utterly without merit and we will defend ourselves vigorously,” she e-mailed. “Multicultural marketing is a common practice in the ad industry and helps brands reach audiences with more relevant advertising. Our policies prohibit using our targeting options to discriminate, and they require compliance with the law.”

Grdina did not immediately respond to Ars’ further questions, but she did point us to an October 28 Facebook post by the company’s head of multicultural marketing, Christian Martinez, who responded to the ProPublica story.

“This kind of communication is positive: it reflects an advertiser's respect for the diverse communities it is trying to reach,” he wrote. “But it's important to know that there's also negative exclusion—for example, an apartment building that won't rent to black people or an employer that only hires men. Our ad policies strictly prohibit this kind of advertising, and it's against the law.”