Proposed rules to help the FBI catch terrorists could lead to innocent Americans being spied upon by government agents or informants "all without any basis for suspicion," a group of Democratic senators said Wednesday. The rules, known as the attorney general guidelines, have not been approved or even publicly released yet, but four Democrats joined a growing chorus of lawmakers raising concerns after being briefed on what the guidelines say. Among their fears: Americans could be targeted in part based on their race, ethnicity or religion - or free speech activities protected by the US Constitution. "As you know, attorney general guidelines were first implemented in the wake of the FBI abuses of the 1960's and 1970's, and serve as one of the most important bulwarks against future abuses," the senators said in a letter to Attorney General Michael Mukasey. The four Democrats - Sens. Dick Durbin, Russ Feingold, Edward M. Kennedy and Sheldon Whitehouse - indicated they remained concerned even after reassurances from officials during the Justice Department briefings.