Declan McCullagh/CNET

The Foreign Intelligence Surveillance Court, the secretive US court responsible for reviewing NSA activities, has published a newly declassified opinion explaining the legal justification behind the foreign surveillance agency's mass collection of phone records.

The National Security Agency is permitted to collect aggregated phone data under Section 215 of the Patriot Act as long as the government can show it relates to known or unknown terrorists in the United States, the court said in a heavily redacted opinion dated August 29. The 29-page opinion (see below) signed by FISC Judge Clair Eagan is the first public opinion to address the constitutionality of the agency's data collection program.

"Because it is necessary to obtain the bulk collection of a telephone company's metadata to determine those connections between known and unknown international terrorist operatives as part of authorized investigations, the production of the information sought meets the standard for relevance under Section 215," Eagan wrote.

In contrast to the Stored Communications Act, which also allows the government access to records, Eagan writes that under Section 215 a request for non-content records "requires neither 'specific and articulable facts' nor does it require that the information be material. Rather it merely requires a statement of facts showing that there are reasonable grounds to believe that the records sought are relevant to the investigation."

Noting that Congress removed the "specific and articulable facts" requirement, Eagan said the government need not "demonstrate any connection to a particular suspect, nor show materiality when requesting business records under Section 215. To find otherwise would be to impose a higher burden -- one that Congress knew how to include in Section 215, but chose to dispense with."

The opinion also points out that Section 215 has a mechanism in place that allows recipients of orders to challenge them, but that none ever has.

"To this date, no holder of records who has received an Order to produce bulk telephony metadata has challenged the legality of such an Order," Eagan wrote in the ruling. "Indeed, no recipient of any Section 215 Order has challenged the legality of such an Order, despite the explicit statutory mechanism for doing so."

The court also concluded that the agency's collection of phone data did not conflict with Americans' Fourth Amendment rights under the third-party doctrine in Smith v. Maryland, a 1979 Supreme Court decision that upheld the collection of electronic communications without a warrant.

"The Supreme Court concluded that a person does not have a legitimate expectation of privacy in telephone numbers dialed, and there, when the government obtained that dialing information, it 'was not a 'search,' and no warrant was required' under the Fourth Amendment," Eagan explained.

The Obama administration, which has defended the NSA activities, has promised to initiate programs to assuage concerns among Americans and foreigners regarding the legality of U.S. surveillance activities.

FISA Declassified Opinion Re Phone Records