An organization of federal agents blasted an anonymous senator who is blocking a bill that would clarify how agents are allowed to assist in responding to major incidents such as the elementary school shooting in Connecticut.

According to the Federal Law Enforcement Officers Association, an unknown U.S. senator placed what is known as a "hold" on the Investigative Assistance for Violent Crimes Act. The bill is one the Federal Bureau of Investigation sought to clarify that federal law enforcement agents are acting in the scope...