Attorney General Michael Mukasey has agreed to postpone implementation of new FBI guidelines, after four Democratic senators raised concerns in a letter Wednesday about proposed changes that they say could permit the FBI to launch investigations of American citizens without any individualized basis for suspicion.

The letter, signed by Sens. Russ Feingold (D-WI), Ted Kennedy (D-MA), Dick Durbin (D-IL), and Sheldon Whitehouse (D-RI), concerned a draft of the Attorney General's Guidelines governing criminal and intelligence inquiries by the Federal Bureau of Investigation. The draft itself has not been made public, though The New York Times reports that the guidelines could be released next month.

The proposed rule change, first reported last week, would loosen restrictions on information sharing between agencies, and allow investigators to begin gathering information for criminal or intelligence purpose, even in the absence of any particularized evidence suggesting that a target is connected to criminal activity.

The senators fear that the new rules "might, for example, permit the FBI to conduct long-term physical surveillance of an innocent American citizen; interview such an individual’s neighbors and professional colleagues, including based on a 'pretext' or misrepresentation; recruit human sources to provide information on that individual; or conduct commercial database searches on that individual—all without any basis for suspicion."

In a speech earlier this month, Mukasey defended the change as a helpful clarification and harmonization of the rules that would better codify existing practices and eliminate "artificial distinctions" between criminal and intelligence inquiries. But Michael German, a former FBI agent now at the American Civil Liberties Union, offered a more skeptical take, calling this characterization a tacit admission that the Bureau had already been ignoring its own guidelines.

Pointing to the case of Stephen Hatfill, whose reputation suffered after he was identified as a "person of interest" in the FBI's investigation into the 2001 anthrax attacks, German said that "opening an investigation against someone has real consequences." While probable cause would still be required to conduct more intrusive searches, German noted that the resources of the FBI could permit it to gather large amounts of nominally "public" information about a target that would be unavailable to a normal private entity. Calling increased reliance on data mining a symptom of "lazy law enforcement," German said that the proposed guidelines are "one more example of the government's failed policies that aren't getting any results, but are eating up a lot of resources and having an affect on innocent people who haven't done anything wrong—it's like a trifecta."

In a response to the senators' concerns addressed to Senate Judiciary Committee Chairman Patrick Leahy (D-VT), Mukasey agreed not to sign off on the new rules until after mid-September hearings at which FBI Director Robert Mueller will testify. Mukasey set a target date of October 1 for making the guidelines effective.