(CNN) Questions remain about a controversial program that monitors American travelers who are not on any terror watchlists nor are suspected of terrorism or criminal behavior, despite changes the Transportation Security Administration has made to how it tracks them.

Marshals will continue to follow and monitor those they identify as persons of interest, but they are changing the threshold for reporting their observations to intelligence agencies, according to TSA.

If an individual does nothing notable on the flight, the marshal will no longer send what they call an after action report, the agency said.

The vague purpose and guidelines sparked criticism of the Quiet Skies program after it was revealed by The Boston Globe earlier this year. Armed undercover air marshals monitor "whether travelers use a phone, go to the bathroom, chat with others, or change clothes," the Globe reported, citing interviews and internal documents.

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