Earlier this week, an investigation from the Boston Globe uncovered a TSA program spanning the past eight years that saw federal air marshals secretly following and monitoring U.S. citizens as they flew between domestic destinations. The program, called “Quiet Skies,” had gone undisclosed since its inception in 2010 and remains active today.

The program sees air marshals identifying passengers that present “suspicious behavior.” Once a martial has determined someone’s behavior to be suspicious, they secretly follow and observe the passenger to ensure they don’t pose a threat to the safety of others. The endeavor, then, seems somewhat innocuous, but some have raised concerns regarding the breadth of behavior that could be deemed suspicious. Air marshals have begun following and reporting on the behavior of Americans for things as slight as sweating more than others in the room or making frequent trips to the bathroom.

“We are no different than the cop on the corner who is placed there because there is an increased possibility that something might happen,” TSA spokesman James O. Gregory said. “When you’re in a tube at 30,000 feet … it makes sense to put someone there.”

Gregory declined to offer more information regarding how marshals identify targets of this program, but he did add that the effort includes using previous travel records and other information available to the TSA to identify targets. Those targets, while often subject to additional screening or checks at airport security, often also have air marshals follow them, even onto the flight, and then provide detailed reports of the target’s activities back to the agency upon the completion of the trip.

Marshals that spoke to the Boston Globe anonymously voiced their own concerns about the program, citing a number of situations where they followed and reported on people that posed no threat to anyone’s safety — including a Southwest Airlines flight attendant and, disconcertingly, one passenger who turned out to be a federal law enforcement agent. These situations would seem to suggest that targets of the Quiet Skies program are not always chosen based on their travel records or identity, but rather simple observational ques. According to the TSA, thousands of Americans have been under observation thus far in the Quiet Skies program, with the details of those reports held by the TSA.

“What we are doing [in Quiet Skies] is troubling and raising some serious questions as to the validity and legality of what we are doing and how we are doing it,” one air marshal wrote. On average, according to the TSA, 35 Americans are targeted and spied upon on domestic flights each day.

Some have characterized this broad approach of targeting and surveillance as a violation of privacy executed by a government agency, and objectively, being followed in secret and having the details of your behavior throughout a domestic trip reported quietly back to the federal government because you’re sweaty or are having a bout of indigestion does sound like a more nefarious violation of privacy than Gregory’s comparison to a “cop on the corner.”

“If that person does all that stuff, and the airplane lands safely and they move on, the behavior will be noted, but they will not be approached or apprehended,” Gregory explained — seemingly suggesting that even passengers that prove to have no malicious intent still have the details of their trip recorded and retained in federal records. When pressed to offer any positive outcomes the Quiet Skies program has led to, including any arrests or incidents that have been averted, Gregory declined to respond.

According to the marshals tasked with the reconnaissance, they often have little idea of why a passenger was chosen — they receive a file containing the passenger’s photo and basic information like birth date and are then tasked with tailing that passenger through the duration of their journey.

The lack of transparency truly seems to be the crux of complaints against this secret endeavor, as the TSA has offered little information regarding how passengers are targetted, what information is collected, or what comes of that information once it has been submitted to the agency.

“If this was about foreign citizens, the government would have considerable power. But if it’s U.S. citizens — U.S. citizens don’t lose their rights simply because they are in an airplane at 30,000 feet,” George Washington University law professor Jonathan Turley said of the program. “There may be indeed constitutional issues here depending on how restrictive or intrusive these measures are.”