Former NSA Director Michael Hayden challenged Leon's conclusion.
"If part of his constitutional ruling is the intelligence utility of the program, he's not in a good position to judge that," Hayden said in an interview. "He makes a judgment that the government was not able to show that this stopped an imminent terrorist attack. That's not the only metric," as metadata also helps intelligence analysts understand their adversaries and track their networks and behavior.
Hayden also downplayed the potential impact of the ruling, saying it seemed to apply only to this one case, rather than setting a legal precedent that would affect NSA operations.
The injunction applies only to the two individual plaintiffs, but it's likely to open the door to much broader challenges to the records collection and storage.
The collection program was disclosed by former NSA systems analyst Edward Snowden, provoking a heated national and international debate. Snowden, in a statement sent to reporter Glenn Greenwald and obtained by The Associated Press, said: "I acted on my belief that the NSA's mass surveillance programs would not withstand a constitutional challenge and that the American public deserved a chance to see these issues determined by open courts. Today, a secret program authorized by a secret court was, when exposed to the light of day, found to violate Americans' rights. It is the first of many."
Klayman said in a telephone interview that it was a big day for the country.
"Obviously it's a great ruling and a correct ruling, and the first time that in a long time that a court has stepped in to prevent the tyranny of the other two branches of government," he said.
Andrew C. Ames, a spokesman for the Justice Department's National Security Division, said in a statement, "We've seen the opinion and are studying it. We believe the program is constitutional as previous judges have found. We have no further comment at this time."