For several years, the National Security Agency unlawfully gathered tens of thousands of e-mails and other electronic communications between Americans as part of a now-revised collection method, according to a 2011 secret court opinion.

The redacted 85-page opinion, which was declassified by U.S. intelligence officials on Wednesday, states that, based on NSA estimates, the spy agency may have been collecting as many as 56,000 “wholly domestic” communications each year.

In a strongly worded opinion, the chief judge of the Foreign Intelligence Surveillance Court expressed consternation at what he saw as a pattern of misleading statements by the government and hinted that the NSA possibly violated a criminal law against spying on Americans.

“For the first time, the government has now advised the court that the volume and nature of the information it has been collecting is fundamentally different from what the court had been led to believe,” John D. Bates, then the surveillance court’s chief judge, wrote in his Oct. 3, 2011, opinion.

The court, which meets in secret, oversees the Foreign Intelligence Surveillance Act, the law authorizing such surveillance in the United States. It has been criticized by some as a “rubber stamp” for the government, but the opinion makes clear the court does not see itself that way.

Bates’s frustration with the government’s lack of candor extended beyond the program at issue to other NSA surveillance efforts.

“The court is troubled that the government’s revelations regarding NSA’s acquisition of Internet transactions mark the third instance in less than three years in which the government has disclosed a substantial misrepresentation regarding the scope of a major collection program,” Bates wrote in a scathing footnote.

The Washington Post reported last week that the court had ruled the collection method unconstitutional. The declassified opinion sheds new light on the volume of Americans’ communications that were obtained by the NSA and the nature of the violations, as well as the FISA court’s interpretation of the program.

The release marks the first time the government has disclosed a FISA court opinion in response to a Freedom of Information Act lawsuit. The lawsuit was brought a year ago by the Electronic Frontier Foundation, a privacy group.

“It’s unfortunate it took a year of litigation and the most significant leak in American history to finally get them to release this opinion,” said foundation staff attorney Mark Rumold, “but I’m happy that the administration is beginning to take this debate seriously.”

The pressure to release the opinion was heightened by a series of recent revelations about government surveillance based on documents leaked to The Washington Post and Britain’s Guardian newspaper by former NSA contractor Edward Snowden.

Over the past 21 / 2 months, those revelations have reignited a national debate on the balance between privacy and security, and President Obama has promised to assuage concerns about government overreach, in part through more transparency.

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