The Electronic Frontier Foundation has published a remarkable letter (PDF) this morning in which the Department of Justice admits its lawyer misled a panel of judges during oral arguments last month over the legality of National Security Letters, or NSLs.

To the surprise of some observers, during his rebuttal, Justice Department lawyer Douglas Letter told the three judges that recipients of NSLs could, in fact, speak about the letters in general terms. They could discuss the fact that they had received a letter and could engage in public debate about the "quality" of the NSLs they had received, he said.

But actually, they can't. Letter's statements contradicted longstanding policy, and EFF apparently asked the DOJ for clarification. The result is that DOJ has sent a note to the Clerk of Court for the 9th Circuit to correct the error, clearing up "an inadvertent misstatement by government counsel during the rebuttal portion of the argument."

Companies are only allowed to talk about their receipt of NSLs and other "national security processes" in "bands." For instance, Google reports having received between 0 and 999 NSLs each year. Alternatively, a company can say it's in a "band" of 0 to 249 if it uses a more vague description category.

"[A]pproximately 49 minutes into the Court’s recording of the argument, government counsel indicated that if a company discloses that it is in one of these two bands starting with zero, it could publicly discuss the fact that it had received one or more NSLs and could discuss the quality of the specific NSL(s) that it had received," explained DOJ. "That suggestion was mistaken."

In other words, the inclusion of zero in the lower "band" isn't an accident. It's deliberate, to make sure the great majority of companies can't say whether they've received one or not.

"We regret this inadvertent inaccuracy and apologize for any confusion that may have been caused," concludes the letter, which is signed by Jonathan Levy, an appellate lawyer in the DOJ's Civil Division.

"During oral arguments we were surprised to hear the government retreat from its position that NSLs gag recipients from talking about the ‘very fact of having received’ an NSL," said EFF legal director Cindy Cohn. "But now we learn that the government’s position remains unchanged. Because the government’s argument to the Ninth Circuit depended in part on the assertion that the NSL gag order does nothing to stifle public debate, this later retraction significantly undermines its case."

Letter's exact words during his erroneous rebuttal, which begins around minute 49 of the recording of the argument (MP3), were as follows: