Following 9/11 fears of terrorism lead the Federal Bureau of Investigation to restrict prisoners' access to religious books. To counteract the threat of radical religious groups recruiting members, gaining influence, or promoting terrorist ideas in U.S. prisons, the Federal Bureau of Prisons compiled list of around 150 "noncontroversial" books and multimedia materials for each of twenty major religions. Materials not included on this list were to be removed from prison libraries. The move brought together outraged prisoners, conservative advocates of religious freedom, and liberal supporters of civil liberties opposed to these restrictions.