The FBI has been illegally obtaining information on the US public, a report by the justice department's inspector general has said.
The attorney general has ordered new safeguards
The FBI used the Patriot Act, passed after the 11 September 2001 attacks, to compel the release of information illegally or improperly, it said.
It said most of the errors were through poor record-keeping or agent mistakes rather than criminal misconduct.
The errors were "unacceptable" and would be corrected, the FBI said.
Rise in requests
The 126-page report by inspector general Glenn Fine said in some cases agents had failed to get the proper authorisation to obtain personal data.
In others they sought the data in non-emergency situations.
"We believe the improper or illegal uses we found involve serious misuses of national security letter authorities," it concluded.
The Patriot Act allowed for the use of such national security letters, or administrative subpoenas, in cases relating to spying or terrorism.
Under such a subpoena, personal records of clients and customers must be handed over to the FBI from such sources as banks, telephone firms and internet service providers.
The report said national security letter requests had risen from 39,000 in 2003 to about 56,000 in 2004 before falling back to about 47,000 in 2005.
In a review of field office files, the report found that 22% of the cases it investigated contained one or more possible unreported or unidentified violations.
Attorney General Alberto Gonzales praised the report and said he had told FBI director Robert Mueller past mistakes would "not be tolerated".
Mr Mueller said the deficiencies were "unacceptable".
"While we've already taken some steps to address these shortcomings, I am ordering additional corrective measures to be taken immediately," he said.