A secret U.S. surveillance program that was revealed to the public by former National Security Agency contractor Edward Snowden has been at least temporarily halted, according to a senior congressional aide.

The NSA program, which involved the mass collection of information about phone calls, has not been used over the past six months, the aide, Luke Murry, said in a podcast interview.

Murry, a specialist in national security who works for California GOP Rep. Kevin McCarthy, did not go into detail about why the program was halted but mentioned “problems” with the way information was collected.

McCarthy’s office would not comment Tuesday beyond a written statement that noted Murry was not speaking on behalf of the Trump administration when he gave the interview to the Lawfare podcast.

The White House and NSA declined comment.

The U.S. began bulk data collection of the time, length and participants — but not the content — of phone calls as part of a surveillance program started after the Sept. 11 attacks. The program prompted widespread controversy after it was publicly exposed by Snowden in 2013.

Authority for the program is due to expire this year unless Congress renews it.

Civil liberties advocates from across the political spectrum have said the program was overly broad and invasive, violating people’s privacy as it swept up call records.

“The NSA should not restart this program if it indeed has sat idle, and Congress should put an end to the program and others like it once and for all,” said Neema Singh Guliani, senior legislative counsel for the American Civil Liberties Union.

Murry said in the podcast, which ran over the weekend, that he considers the collection program “critical” to national security but is not sure the administration will seek to resume it.

Oregon Sen. Ron Wyden, a Democrat who has been critical of the surveillance program, said the NSA should let the public know if it has been halted.

“The administration must permanently end the phone records program and Congress should refuse to reauthorize it later this year,” Wyden said.

David Greene, senior staff attorney and civil liberties director at San Francisco, California-based Electronic Frontier Foundation, said there were many reasons why the program shouldn’t be renewed.

“Even in its more limited form, the program sucks up a lot of records of people not suspected of doing anything wrong,” he said.

If the Trump administration advocates for its demise, “I would hope that Congress would let it go,” Greene said.

He said technical problems have made it difficult to comply with the law, and that the program is costly to administer, but that it’s too early to know why the administration would want to scrap the program.

In 2015, Congress changed the law so that the NSA must request the information from the telecom providers rather than sweep it up in a wholesale fashion. Still, critics want to see further changes to prevent what they see as large-scale surveillance that infringes on civil liberties.

The NSA collected more than 534.4 million details of calls and text messages in 2017 from American telecom providers like AT&T and Verizon, according to the most recent government report covering NSA surveillance activities. That was more than three times the 151.2 million collected in 2016.

(AP)