A bipartisan coalition of lawmakers is asking the Department of Homeland Security’s internal watchdog to investigate the Transportation Security Administration’s use of facial recognition technology over concerns about the agency’s collection of biometric data.

On a Wednesday letter to DHS Inspector General Joseph Cuffari, 12 senators — seven Democrats and five Republicans — called for a thorough review of how the TSA uses facial recognition to verify travelers’ identities “from both an agency and privacy perspective.”

“This technology will soon be deployed at hundreds of large and medium-sized airports without an independent evaluation of the technology’s accuracy or a review of whether adequate safeguards are in place to protect passenger privacy,” the senators wrote.

The TSA has already implemented facial recognition technology at more than 80 airports that compares real-time photos of travelers to their government-issued ID. The agency plans to expand the use of facial biometrics to more than 400 airports in the coming years, though some lawmakers and privacy rights groups have expressed concern about the widespread deployment of the technology.

TSA and DHS officials told Nextgov/FCW earlier this year that the agency has signs around the airport alerting travelers to the use of facial recognition and disclosing their right to opt out of the screening if they choose to do so. The officials also emphasized that travelers’ personal information is not stored by the screening machines, except in “limited testing environments.”

The lawmakers’ letter said that, although facial recognition screenings are optional for travelers, transportation security officials are “inconsistently trained on how to respond to passengers requesting to opt out and have told passengers they will face delays for opting out.”

If facial biometrics is rolled out to every US airport, the lawmakers also warned that the program “could become one of the largest federal surveillance databases overnight without authorization from Congress.”

In the letter, DHS asked the IG to specifically examine the effectiveness of TSA’s facial recognition technology, including its “collection and storage of travelers’ biometric data and determining when and if TSA deletes this information after passenger verification.”

TSA Administrator David Pekoske said during a House hearing in May that it could take the agency about 25 years to fully implement the facial recognition technology if lawmakers did not stop the diversion of 9/11 security fees away from the agency.

If the agency receives its full allocated funding, Pekoske said the rollout of the new tools could be completed by the end of this decade, as the TSA already “has the vendors and processes in place” to fully implement the facial recognition technology.

Several of the letter’s signatories — including Sens. Jeff Merkley, D-Ore., John Kennedy, R-La., and Sen. Roger Marshall, R-Kan. — earlier proposed a measure in May that would have paused the TSA’s rollout of facial recognition technology at additional airports until Congress had a chance to review the initiative.

Lawmakers hoped to attach their amendment to legislation reauthorizing the Federal Aviation Administration, though their provision was ultimately removed from the final package.