A nonprofit housing group has filed a lawsuit against several local real estate agents and Web sites, claiming their online advertising uses discriminatory phrases in seeking renters.

In the suit filed in U.S. District Court in Boston on Tuesday, the Fair Housing Center of Greater Boston said phrases such as "professionals only," "no undergrads please!" and "no security deposit required with good credit and stable employment" violate federal and state laws.

Those statutes make it illegal to advertise any preference, limitation or discrimination based on race, color, religion, sex, handicap, family status or national origin.

The suit seeks injunctive relief and unspecified monetary damages.

"The effect of these advertisements has been to restrict the housing choices and opportunities for families with children and persons with rental subsidies," the housing group's complaint said. "Further, because a disproportionate number of persons with rental subsidies and families with children are people of color, these advertisements have had the effect of discriminating against people based on race, color and national origin."

Several defendants in the suit denied wrongdoing, and said they first heard of the complaint when contacted by The Boston Globe.

"I know all about discrimination," said Marc Roos, the owner of Marc Roos Realty in Boston, who described himself as an Iranian immigrant who is a U.S. citizen. "The last thing I want to do is anything discriminatory."

Eric Boyer, who operates Boston Apartment Rentals and an accompanying Web site called bostonapartments.com that posts real estate ads, said he never would knowingly allow a discriminatory ad to be posted on the Web site.

He described the Web site as "a free-form bulletin board," and said he does not edit ads posted on the site.

Representatives for two other defendants, A&S Realty and Apartment Depot, declined to comment when reached by the Globe.

In 2001, the Globe agreed to settle a cimilar complaint by the Fair Housing Center, which claimed that it published ads that included such phrases as "single pref" and "no Section 8," a reference to a rent-subsidy program.

Under the settlement, the newspaper paid the center $30,000 to support fair housing education programs, and $25,000 for damages and attorneys fees. The Globe also agreed to tighten its housing ad policies.