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.