That was the question yesterday before a federal appeals court in San Francisco, where government lawyers argued that National Security Letters — FBI requests for information that are so secret they can't be publicly acknowledged by the recipients — were essential to counterterrorism investigations. The telecom company and internet provider that have challenged the National Security Letters (known as NSLs) still can't even be named.

Last year, in a sharp rebuke to the government, a judge found that the gag order that comes with NSLs violated the First Amendment. The nondisclosure rule "significantly infringe[s] on speech regarding controversial government powers," U.S. District Judge Susan Illston, of Northern California, wrote in March 2013. She also ordered that the FBI stop sending out NSLs entirely, but put the order on hold to give the government a chance to appeal.