The Federal Bureau of Investigation has taken on everyone from Al Capone to John Dillinger to the Unabomber. Its latest adversary: Wikipedia.

The bureau wrote a letter in July to the Wikimedia Foundation, the parent organization of Wikipedia, demanding that it take down an image of the F.B.I. seal accompanying an article on the bureau, and threatened litigation: “Failure to comply may result in further legal action. We appreciate your timely attention to this matter.”

The problem, those at Wikipedia say, is that the law cited in the F.B.I.’s letter is largely about keeping people from flashing fake badges or profiting from the use of the seal, and not about posting images on noncommercial Web sites. Many sites, including the online version of the Encyclopedia Britannica, display the seal.