ProPublica reporters last week bought dozens of rental housing ads on Facebook, but asked that they not be shown to certain categories of users.
They wanted to investigate whether Facebook allows housing advertisers to exclude African Americans, mothers of high school kids, people interested in wheelchair ramps, Jews, expats from Argentina and Spanish speakers.
All of these groups are protected under the federal Fair Housing Act, which makes it illegal to publish any advertisement "with respect to the sale or rental of a dwelling that indicates any preference, limitation, or discrimination "
But ProPublica said all of its ads were approved within minutes.
The only advertisement that took longer than three minutes to get approval sought to exclude potential renters "interested in Islam, Sunni Islam and Shia Islam."
It was, however, approved within half an hour.
Under its own policies, Facebook should have flagged these ads, and prevented the posting of some of them, ProPublica said on Tuesday.
Facebook, however, called it a "technical failure".
"This was a failure in our enforcement and we're disappointed that we fell short of our commitments," Ami Vora, Vice President of Product Management at Facebook, was quoted as saying.
"The rental housing ads purchased by ProPublica should have but did not trigger the extra review and certifications we put in place due to a technical failure," Vora added.
An earlier investigation by ProPublica this year showed that the social network also enabled advertisers to reach "Jew haters".
(This story has not been edited by NDTV staff and is auto-generated from a syndicated feed.)