U.S. citizens wary of facial biometric technology can opt-out of Customs and Border Protection’s face-scanning programs, though that would change under a proposed rule.

CBP has been pushing the use of facial recognition technologies at land, sea and air ports as a means of meeting a longstanding congressional mandate to use biometrics in the entry/exit process. That includes in-motion imaging of everyone coming into the country at airports and other select ports of entry as well as during the boarding process for international flights.

Outbound travelers were first introduced to the facial recognition at Dulles International Airport in September 2018, though the program has expanded to more than 20 ports of entry across the country. At airports, as passengers move to board the plane, a tablet computer set up near the gate captures an image of the traveler’s face and matches it to the plane’s manifest, which includes photos taken from the traveler’s documents, such as a passport.

But U.S. citizens and green card holders currently have the option to decline this biometric scan and opt for traditional boarding procedures instead. That would change under a proposed rule filed with the Office of Information and Regulatory Affairs.

“To facilitate the implementation of a seamless biometric entry-exit system that uses facial recognition and to help prevent persons attempting to fraudulently use U.S. travel documents and identify criminals and known or suspected terrorists, [the Homeland Security Department] is proposing to amend the regulations to provide that all travelers, including U.S. citizens, may be required to be photographed upon entry and/or departure,” according to the rule change filing.

The proposed policy change was first reported by TechCrunch.

Privacy advocates are pushing back against the new rule, including lawmakers like Sen. Edward Markey, D-Mass.

“The Department of Homeland Security should immediately withdraw plans to force Americans to undergo facial recognition and hand over their biometric information,” he said in a statement Tuesday. “This proposal would amount to disturbing government coercion, and as the recent data breach at Customs and Border Protection shows, Homeland Security cannot be trusted to keep our information safe and secure. I will soon introduce legislation to ensure that innocent American citizens are never forced to hand over their facial recognition information.”

Markey said he has been working with Sen. Mike Lee, R-Utah, to get additional information from CBP on the agency’s use of biometric technologies.

In a statement Wednesday, the agency reasserted its commitment to protecting travelers’ privacy and addressing concerns.

“U.S. Customs and Border Protection is using biometric facial comparison technology to facilitate the entry and exit of international travelers while meeting the congressional mandate to implement a biometric entry-exit system,” a CBP spokesperson told Nextgov. “U.S. citizens are out of scope of the mandated biometric entry-exit program. However, U.S. citizens are required to establish identity and citizenship to CBP and present a valid U.S. passport for international travel.”

The notice of the proposed rule change sets the timeline for it to go into effect by July 2020. However, the spokesperson told Nextgov the agency is still in the early stages and no changes will be made without going through the long regulatory change process, which will include periods for public comment.