SAN FRANCISCO — The Congressional Black Caucus has called on Facebook to stop allowing advertisers to exclude racial and ethnic groups when placing housing ads in what lawmakers say is a violation of federal anti-discrimination housing laws.

"We are writing to express our deep concerns with reports that Facebook’s 'Ethnic Affinities' advertising customization feature allows for advertisers to exclude specific racial and ethnic groups when placing housing advertisements," members of the caucus wrote in a letter addressed to Facebook's chief executive Mark Zuckerberg on Tuesday.

“This is in direct violation of the Fair Housing Act of 1968, and it is our strong desire to see Facebook address this issue immediately," reads the letter.

In an emailed statement, Facebook said: "Multicultural marketing is a common practice in the ad industry and helps brands reach audiences with more relevant advertising. We've heard from groups and policy makers who are concerned about some of the ways our targeting tools could be used by advertisers. We are listening and working to better understand these concerns."

The letter from the Congressional Black Caucus came in response to Friday's Pro Publica report that Facebook advertisers can exclude specific racial and ethnic groups when placing housing ads in potential violation of the Fair Housing Act of 1968, according to a Pro Publica report.

Using a designation called "Ethnic Affinities," Facebook lets advertisers target and exclude certain groups of Facebook users when placing ads for a new apartment or a house for sale. Pro Publica says it placed an ad for a housing-related event that excluded African Americans, Asian Americans, and Hispanics.

Facebook says it bans advertisers from using "Ethnic Affinities" to discriminate against racial or ethnic groups.

According to the Fair Housing Act of 1968, it's illegal "to make, print, or publish, or cause to be made, printed, or published any notice, statement, or advertisement, with respect to the sale or rental of a dwelling that indicates any preference, limitation, or discrimination based on race, color, religion, sex, handicap, familial status, or national origin."

University of Connecticut law professor Jon Bauer says if Facebook allows housing ads to be targeted in a way that excludes racial and ethnic groups, "they are clearly violating the Fair Housing Act of 1968." The same would hold true for other areas covered by civil rights legislation such as employment, Bauer said.

In its letter to Zuckerberg, the Congressional Black Caucus also called on Facebook to make a stronger commitment to diversifying its workforce.

"With 2% of Facebook’s U.S. employees being African-American, and 4% Hispanic, we remain convinced that a stronger commitment to diversifying the ranks of your company especially in senior management positions to better reflect the diversity of your 1.7 billion monthly users will help in ensuring that innovative and inclusive platforms continue to be promoted by your company,” the lawmakers wrote to Zuckerberg.

Like other major Silicon Valley technology companies, Facebook is wrestling with its lack of diversity.

The percentages of African-American and Latino workers have not budged since 2014 and fall below other industries' averages. Facebook has made slightly more progress on gender diversity, yet nearly seven out of 10 employees around the globe are men.