Privacy advocates are up in arms after the Department of Homeland Security unveiled a facial recognition pilot program for surveilling public areas surrounding the White House.

The program, outlined last week, will use biometrics to confirm the identity of various U.S. Secret Service (USSS) employees, separating them from members of the public. The Secret Service also said that video streams from selected cameras in two public places around the White House will capture individuals on the sidewalk and street. The facial recognition pilot will then identify “subjects of interest.”

“Ultimately, the goal of the [Facial Recognition Pilot] is to identify if facial-recognition technologies can be of assistance to the USSS in identifying known subjects of interest prior to initial contact with law enforcement at the White House Complex,” according to the Department of Homeland Security in a privacy impact assessment (PIA) of the pilot. “The collection of volunteer subject data will assist USSS in testing the ability of facial recognition technology to identify known individuals and to determine if biometric technology can be incorporated into the continuously evolving security plan at the White House complex.”

Experts however are concerned about the pilot’s impact on privacy. Jay Stanley, senior policy analyst at the American Civil Liberties Union, on Tuesday said that the pilot represents a “milestone.”

“Physical protection of the president and the White House is not only a legitimate goal but a vital one for protecting the stability of our republic,” said Stanley. “And while this pilot program seems to be a relatively narrowly defined test that does not in itself pose a significant threat to privacy, it crosses an important line by opening the door to the mass, suspicionless scrutiny of Americans on public sidewalks.”

Stanley voiced a number of concerns with this latest pilot program in the White House: For instance, what if people are falsely matched to target subjects? And what exactly constitutes a “subject of interest?”

The Department of Homeland Security addressed concerns that members of the public may be unaware that their facial images are being captured and used by a facial recognition technology, by saying that the risk is “partially mitigated.”

“General notice is provided to the public by this PIA,” the department said. “The USSS volunteer employees participating in the pilot are provided individual notice and have consented to their participation. Facial images determined not to be a match to images in the USSS gallery will be immediately deleted from the FRP [facial recognition pilot] system.”

The DHS said that data collected will be stored in a stand-alone database dedicated to the pilot testing and not made available for routine use in supporting Secret Service operations. Upon completion of the pilot, all remaining collected facial images will be deleted.

However, the department said that the public cannot opt-out of the facial recognition pilot, except to avoid the areas that will be filmed as part of the program.

The Secret Service’s efforts are the latest government use case for facial-recognition technology. In 2017, U.S. Customs and Border Protection launched a “Traveler Verification Service” that applies face recognition to all airline passengers, including U.S. citizens, boarding flights exiting the United States. The Transportation Security Administration in 2018 released plans to expand facial surveillance technology across more airports broadly.

More tech giants are also tapping into the lucrative applications that facial recognition technology has to offer. Amazon’s Rekognition platform has utilized the technology to sniff out large numbers of people in a single video or still frame.

Stanley urged policymakers to think carefully about the dangers of facial-recognition technology as the tech continues to grow in popularity.

“The program is another blinking red light for policymakers in the face of powerful surveillance technologies that will present enormous temptations for abuse and overuse,” said Stanley. “Congress should demand answers about this new program and the government’s other uses of face recognition. And it should intercede to stop the use of this technology unless it can be deployed without compromising fundamental liberties.”