The Foreign Intelligence Surveillance Court, often called the FISA Court after the 1979 law that created it, has approved more than 99 percent of government warrant requests, presiding Judge Reggie Walton told Senate Foreign Relations Committee Chairman Patrick Leahy, D-Vt., and seven other Senate and House committee heads and ranking members.
It has turned down no warrant requests in the past four years and denied just 10 of the 34,000 applications it has received since its 1978 inception.
But what the raw figures don't show is the back and forth between the court and the Justice Department over its requests, Walton said in the letter, which can be found at tinyurl.com/UPI-Walton-letter.
The court, whose opinions are usually kept secret, faced criticism after British newspaper The Guardian and The Washington Post reported it secretly approved the broad, sweeping, daily collection of Americans' phone records, including those for domestic calls.
Critics called the court a rubber-stamp institution, with considerable power under the law but little power in practice.
U.S. officials responded, arguing the National Security Agency's surveillance programs were legal and subject to rigorous judicial oversight.
Walton said in his letter he believed a sample period would illustrate the way the court generally works.
"During the three-month period from July 1, 2013, through Sept. 30, 2013, we have observed that 24.4 percent of matters submitted ultimately involved substantive changes to the information provided by the government or to the authorities granted as a result of court inquiry or action," Walton's letter said in the letter dated Friday but posted to the court's website Tuesday.
"This does not include, for example, mere typographical corrections," the letter said.
But Walton conceded the pre-approval modifications were a result of an informal back and forth between the Justice Department and the court, so it may be hard to objectively attribute the substantial changes to the court's actions.
"[T]hese statistics are an attempt to measure the details of what are, typically, informal communications between the branches," Walton wrote. "Therefore, the determination of exactly when a modification is 'substantial,' and whether it was caused solely by the [court's] intervention, can be a judgment call."
On the day Walton sent the letter, the court approved another 90-day request for millions of Americans' phone data, the Office of the Director of National Intelligence, which oversees the NSA, said in a statement.