The FBI may have illegally obtained thousands of phone records between 2002 and 2006. An investigation indicates FBI agents persuaded phone companies to turn over records by claiming terrorism emergencies that did not actually exist. The FBI appears to have compounded the problem by approving the records gathering after the fact.
The FBI has tried to diffuse the situation by explaining, at times, the volume of information on terrorist activities can overwhelm agents. In addition, the FBI’s general counsel explained that agents have a legal right to gather the records in true emergencies.
The FBI has admitted, however, that approving the requests for records after the fact was "good-hearted but not well-thought-out."
FBI broke law for years in phone record searches | Washington Post