SAN FRANCISCO — A California law firm with ties to the National Rifle Association is using public records laws to compile a dossier on the activities of a national group Mayor Bloomberg set up to lobby Congress on gun issues.

Several mayors who have signed onto the Mayors Coalition Against Illegal Guns in recent months report being greeted with formal freedom of information requests from Trutanich Michel LLP, which is based in Los Angeles and San Diego.

“It’s the first FOIA request on any issue I’ve worked on since I’ve been mayor,” Mayor Otto Lee of Sunnyvale said at an event Mr. Bloomberg attended last week in San Francisco. “It’s not at this point terribly annoying, but it has unfortunately disrupted the distribution of services to the community.”

The mayor of San Francisco, Gavin Newsom, reported receiving a similar request. Another official involved with the mayors’ group said Richmond, Calif., had also been asked for all its documents related to the organization.

Two requests obtained by The New York Sun were filed by a Trutanich Michel lawyer, Clint Monfort. No client is named in the requests. Mr. Monfort did not return a phone call and e-mail message seeking comment yesterday afternoon.

A partner at the same law firm, Chuck Michel, is identified on an NRA Web site as “chief attorney for the National Rifle Association (NRA) and the California Rifle and Pistol Association (CRPA) in the Golden State.”

However, a spokesman for the NRA, Andrew Arulanadam, denied that the apparent flurry of public records requests was connected to his organization. “We have nothing to do with the FOIA requests,” he said.

Some of the requests also seek information about a lawyers’ group active in gun control efforts, Lawyers Committee Against Violence.

A spokesman for Mr. Newsom, Joseph Arellano, said the requesters were notable for their persistence. “This one is surprising just because Trutanich continues to send them regardless of our responses. They just keep following up,” Mr. Arellano said. “Even when we’ve told them any communication … is privileged, they keep asking.”

A spokesman for Mr. Bloomberg, Jason Post, declined to comment on the information-gathering effort.

Mr. Bloomberg’s group, which is also led by Mayor Thomas Menino of Boston, is pushing to prevent renewal of the Tiahrt Amendment, a provision authored by Rep. Todd Tiahrt, a Republican of Kansas. The measure limits the ability of local police to use federal gun trace data to determine which gun dealers sell the most weapons used in crimes.

More than 225 mayors have signed up with Mayors Against Illegal Guns. Mayors from four cities — Anchorage, Alaska, Rio Rancho, N.M., Idaho Falls, Idaho, and Williamsport, Pa. — are known to have dropped out after protests from gun rights advocates.

Some of those who quit cited an unusual sting operation in which private agents working for New York attempted to make so-called straw purchases of guns from out-of-state gun dealers.