Under the Fair Housing Act, ads for housing or employment cannot discriminate "based on race, color, religion, sex, handicap, familial status or national origin."
According to BuzzFeed, a representative for Facebook said ProPublica's ad wasn't for housing but for a housing-related event.
"All major brands have strategies to speak to different audiences with culturally relevant creative," the spokesman told BuzzFeed.
Steve Satterfield, Facebook's privacy and public policy manager, said company "policies prohibit using our target options to discriminate, and they require compliance with the law." He also told ProPublica that "ethnic affinity" is not race.