By Rene Marsh, Gregory Wallace and Ellie Kaufman, CNN

(CNN) --

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.

Over the weekend, the paper first reported the changes to the program.

The TSA responded by defending Quiet Skies, telling CNN it "has evolved."

"The only change to the program has been in the reporting mechanism," the agency said.

Sen. Ed Markey, a Democrat from Massachusetts who's a critic of the program, said Monday that he is "pleased that TSA is now scaling back its collection of personal information about innocent Americans and their behavior."

"However, I continue to have concerns about the effectiveness and invasiveness of this program," Markey said.

Critics of the program said the secrecy raises the potential of targeting people based on their races or nationalities. The TSA has said that is not the case.

The American Civil Liberties Union said after the program was revealed that it raises "a host of disturbing questions."

In addition to constitutional concerns, "federal law enforcement shouldn't be tracking and monitoring travelers and then logging detailed information about them without any basis to believe that they've done anything wrong," ACLU attorney Hugh Handeyside wrote in July.

"The safety and security of travelers continues to be the number one focus of TSA; Quiet Skies continues to add another layer of security to achieve that mission," spokeswoman Jenny Burke said Monday in a statement. She said the agency "continually assesses every measure, making adjustments to optimize effectiveness or address evolving threats."

In August, the inspector general for the Department of Homeland Security announced it would review the program.