A federal lawsuit accuses the online site Craigslist of violating fair housing laws by publishing discriminatory classified ads, reviving the question of what legal boundaries, if any, should exist for postings on the Internet.

But legal experts say the lawsuit against Craigslist, a fast-growing online network of classified ads and forums, faces an uphill battle because of laws in place to protect online service providers.

The lawsuit, filed by a Chicago fair housing group in U.S. District Court last Friday, contends that Craigslist's Chicago site distributed more than 100 ads that violated the federal Fair Housing Act by excluding prospective buyers or tenants on the basis of race, gender or religion.

Among the housing ads cited as objectionable by the Chicago Lawyers' Committee for Civil Rights Under Law Inc. were ones that read "NO MINORITIES," "Requirements: Clean Godly Christian Male," and "Only Muslims apply."

While it remained unclear Thursday if the suit is the first of its kind, it signifies a burgeoning effort by housing watchdog groups to extend to the Internet the same legal restrictions facing those that publish print classifieds.

"Our goal is to have the Internet places like Craigslist treated no differently than newspapers and other media who have traditionally been posting real estate advertisements," said Stephen Libowsky, a counsel for the housing group. "All of the gains are going to get lost if the same rules don't apply."

The nonprofit group is an affiliate of the National Fair Housing Alliance. Its Louisiana affiliate, the Greater New Orleans Fair Housing Action Center, recently filed a similar complaint against the hurricane relief Web site Katrinahousing.org, alleging it found 68 discriminatory housing ads.