SINCE leaked documents revealed in June that America’s National Security Agency (NSA) has been collecting information about phone calls made by millions of Americans, citizens and journalists have clamoured to know more. They want to know especially about the Foreign Intelligence Surveillance Act (FISA) court, which since 1978 has approved or declined the agency’s snooping operations by weighing them against the law. On July 6th the New York Times reported that as well as ruling on specific operations the court has been handing down classified decisions on general surveillance issues, many of them favourable to the spies. These rulings constitute a secret body of law, anonymous sources told the Times: rather than holding spies to account, the FISA court is starting to resemble a parallel Supreme Court.

The job of the 11 judges who serve on the court seems to have “changed very dramatically” in recent years, says William Banks, a law professor at Syracuse University. Time once spent weighing the details of individual cases is increasingly spent checking that requests for broad data-collection are legitimate. Of particular significance is the court’s apparent decision that data on all American calls can be considered “relevant” to investigations of terrorist threats. That keeps the NSA’s surveillance programmes within the letter of the law, but relies on stretching “relevance” far wider than its workaday legal sense.

The FISA court does not seem the right forum for this. It hears in secret from government lawyers, but not from those who are being spied on. Critics call it partisan, and it looks it: of the 14 judges who have served on the court in 2013, 12 are Republicans. It looks tame, too: according to congressional reports, between 2001 and 2012 FISA judges approved 20,909 requests to monitor individuals or search properties, turning down only ten. Yet between 2007 and 2012 the court did order changes of an unknown nature to 428 of the 532 requests it received for the collection of business records. Such applications can allow spooks to download huge chunks of call data.

The American Civil Liberties Union, a lobby group, has filed a suit ordering the FISA court to reveal its most pertinent legal rulings. That will be a tough fight. The government may wish to dispel the worst rumours about its spying, but many spymasters are convinced that secrecy helps them catch terrorists.