More needs to be done to ensure the anonymity of federal air marshals, says a critical new report Congress will look into next week.

The draft report, "Plane Clothes: Lack of Anonymity at the Federal Air Marshal Service Compromises Aviation and National Security," cites the service's dress code, which is supposed to prevent marshals from drawing attention to themselves.

In practice, the report found, "many federal air marshals indicate that the dress code actually draws more attention to the identity of the federal air marshals because of its rigid requirements that prevent federal air marshals from actually blending in with their surroundings."

The report by the House Judiciary Committee, a copy of which was provided to The Associated Press on Friday night, identified several policies by the service that the report concluded undercut the goal of preserving the marshals' anonymity.

The report also faults the service for requiring marshals to stay at designated hotels and show their credentials upon checking in. It said that in one instance, the Sheraton Fort Lauderdale Airport Hotel in Florida designated the service "company of the month" because of the number of rooms it had reserved at the hotel.

"This public designation essentially advertises for any terrorist wishing to attack a location populated by a concentration of federal air marshals that such a target is the Sheraton Fort Lauderdale Airport," the report says, referring to the hotel.

And the report raised questions about boarding procedures by marshals, expressing concern that these procedures could give away the identity of the marshals.

The committee, which initiated its investigation into the service in May 2004, said its staff interviewed 30 federal air marshals across the country.

"An overwhelming majority of the interviewed air marshals stated that most concerns centered around threats created by the service's own policies to preserving anonymity and safety," the report says.

The report also found the service's policy banning marshals from criticizing the service too broad, expressing concern that it was being used "as a retaliatory mechanism against those who vocalize legitimate concerns" about the service's policies.

Dave Adams, a spokesman for the service, said he had not seen the report. But he did say that the service "fully cooperated and addressed" concerns and inquiries made by the committee chairman, Wisconsin Republican Jim Sensenbrenner.

Adams said that the service provided a 29-page formal response, as well as a follow-up briefing in November 2004. The service has not been contacted by the committee on any substantive issue since then, he said.

"Anonymity of the air marshals in our No. 1 concern," Adams said. "But the boarding of air marshals is set by federal regulations, which Congress sets."

The committee is expected to vote on the draft report next week.

ABC News first reported on the committee's findings Friday.