The social network not only allows advertisers to target users by their interests or background, it also gives advertisers the ability to exclude specific groups it calls “Ethnic Affinities.” Ads that exclude people based on race, gender and other sensitive factors are prohibited by federal law in housing and employment.

Article source: http://www.huffingtonpost.com/entry/facebook-advertising-racism_us_58136a76e4b0390e69cfa6bf?section=us_technology