National Security Letters -- also known as NSLs -- are a type of administrative subpoena designed to allow the FBI to access the records of people suspected of being foreign agents.
The Justice Department credits the Patriot Act with expanding the government's arsenal of investigative tools, helping it crack several cases. But critics say the law has made it too easy for law enforcement to spy on people. Read about the alleged successes and abuses of the law:
These subpoenas originated in the 1970s, but Section 505 of the Patriot Act -- which was passed shortly after the Sept. 11 attacks -- greatly expanded the FBI's ability to use them.
Under the Patriot Act, a person does not have to be suspected of wrongdoing in order for the FBI to obtain their sensitive financial, communications or other personal records. Instead, FBI agents only have to state that the information they are seeking is "relevant" to a national security investigation. The letters are issued without prior court approval, and recipients are placed under a gag order that prevents them from telling anyone about the demand for records. Last year, the FBI issued 9,254 NSLs, according to the Justice Department.
When Congress reauthorized the Patriot Act earlier this year, it modified rules concerning the use of National Security Letters. Perhaps the biggest change: A recipient of an NSL now has the explicit right to consult a lawyer about the order, and to challenge it in court. A judge can overturn the order if it is "unreasonable," "oppressive" or "otherwise unlawful."
The reauthorized Patriot Act also grants special protections to libraries: Those acting in a traditional role -- as a lending institution, or a place where patrons can access e-mails -- are no longer subject to NSLs. However, these protections don't extend to libraries that act not just as Internet access points but as full-on Internet service providers.
But the law still gives the government the upper hand: If the government certifies that challenging an NSL would harm national security, interfere with an investigation or with diplomatic relations, or endanger someone's life, the court has no choice but to uphold the order. Anyone who violates a gag order "knowingly and with intent to obstruct an investigation or judicial proceeding" could face a prison term of up to five years.
The Justice Department says National Security Letters are a vital tool in the war on terrorism, giving FBI agents the ability to quickly find and pursue leads in anti-terrorism investigations.
But critics say these administrative subpoenas violate Fourth Amendment rights against unreasonable searches and seizures, allowing the FBI to collect information on citizens who are not accused of any wrongdoing.
Supporters say there is no evidence that the FBI has abused these orders. Critics note that, while the reauthorization required the Justice Department to report the actual number of NSLs issued for the first time, more detailed records are either non-existent or are classified.