The U.S. Department of Housing and Urban Development (HUD) announced last week that it has filed a civil complaint against Facebook, Inc. alleging violations of the Fair Housing Act as a result of Facebook’s ad-targeting system. Twitter, Inc. and Google have been notified that their similar practices are under scrutiny.

Facebook’s ad-targeting system allows advertisers the ability to direct messages to target audiences with precision.  HUD charges this system has allowed real estate companies to unlawfully discriminate on the basis of race, nationality, religion, color familial status, sex and disability.

The complaint alleges Facebook is guilty of “encouraging, enabling and causing” unlawful discrimination when it allows advertisers to exclude users by certain characteristics, for example, whether they are interested in Hispanic culture and food, whether they are parents and whether they are non-citizens or non-Christians. Some ads are only shown to women. Other ads may exclude neighborhoods or geographic areas like ZIP codes. Secretary of HUD Ben Carson said using a computer to limit a person’s housing choices can be just as discriminatory as slamming a door in that person’s face.

HUD alleges Facebook mines users’ extensive personal data and uses characteristics protected by law to determine who can view housing ads.

This is not the first time Facebook has been in trouble for ad-targeting. An earlier investigation by ProPublica found the advertising practices acted to exclude African American, Latinos and Asian Americans. HUD had filed an earlier complaint last August alleging ethnic groups were excluded from viewing some ads. Facebook took action by removing 5,000 ad target options.

The ACLU was not happy with that result and filed a lawsuit. That lawsuit was settled recently with Facebook announcing substantial changes to its platform including withholding a wide array of demographic information often used as indicators of race. Facebook also agreed to create a tool that would allow users to search for housing ads whether or not the ads could be viewed in individual news feeds.

HUD was apparently dissatisfied with the settlement as not going far enough to remedy housing discrimination and responded with the current complaint.