A suit filed in a Dayton, Ohio, federal court charges that listing an apartment as a bachelor pad amounts to discrimination.
The ad on Craigslist said the pad would be just the thing for single guys looking to "hook up."
The Miami Valley Fair Housing center is seeking at least $25,000 in damages.
Staffers at the nonprofit center say the ad apparently discriminates on the basis of sex and family status.
But officials with the property owner, The Connor Group, say they expect to be cleared.