CHANGING your clothes in an airport toilet, inspecting your reflection in a terminal shop window or being the last person to board a flight are not normally thought to be unusual behaviours for travellers in an airport. But America’s law enforcement agencies seem to disagree. The Boston Globe, a newspaper, broke the news last weekend of a secret programme of America’s Transportation Security Administration (TSA) called Quiet Skies, under which passengers doing these things are followed, watched and have their actions recorded by air marshals.

The programme, whose existence was only admitted by the TSA after the Globe’s scoop, has been criticised for violating people’s privacy and by people within the agency for wasting their time and diverting them from dealing with genuine threats. “Quiet Skies is the very definition of Big Brother”, said Ed Markey, a senator for Massachusetts. And it does not seem to be very effective. Some marshals have been tasked with following travellers who turn out to be poor targets: in one case, a Southwest Airlines flight attendant; in another, a federal law-enforcement officer.

Marshals are not just shadowing anyone in the airport who looks suspicious. Instead, they track people who have been placed on a Quiet Skies list. The criteria for landing on the list remain murky, but according to an internal memo obtained by the Globe, they include travel patterns or behaviours similar to those of suspected terrorists and possible affiliations with people on the terrorist watch list.

About 5,000 American citizens have been the subject of surveillance under the programme. Every day, 40 to 50 passengers on the Quiet Skies list take flights, and about 35 of them are shadowed by air marshals. The armed marshals file minute-by-minute reports to the TSA on whether the passengers exhibit any suspicious behaviour such as fidgeting, staring, observing the boarding gate area from afar, boarding last, reversing directions, changing clothes, or shaving. They also note whether these passengers sleep during their flights.

This is not the first TSA programme in recent years to raise serious concerns about passenger privacy. In 2015, leaked internal newsletters showed that TSA officers were routinely mocking passengers who did not have a good understanding of security procedures (a group that includes less well-off people who fly less frequently). The same year it was also revealed that TSA officers are flagging passengers based simply on suspicious behaviours such as excessive yawning.

Some air marshals have told their colleagues they find Quiet Skies “troubling” and possibly illegal. That is alarming. Although there is still much that we do not know about the programme, it seems rife with potential for abuse as well as a great waste of taxpayers’ money. On August 2nd the agency admitted that the programme had yet to snare any threats. If air marshals themselves are wary of the new effort, then many flyers are sure to be alarmed at the prospect of yet another secretive programme to track their movements and behaviour while travelling.