Sen. Al Franken (D-Minn.) pressed a Facebook official on Wednesday to provide stronger privacy protections for the company's tool that identifies users' faces.
He argued that Facebook should require that users opt in to the feature, rather than just allowing them to opt out of it.
"I'm worried about how Facebook handles the choices it does give users about this technology," Franken said at a hearing of the Senate Judiciary Committee's subcommittee on Privacy, Technology and the Law, which he chairs.
Facebook began using a tool last year that identifies a user's friends in pictures based on their facial features and suggests that the user should tag them.
Facebook has since pulled the photo-tagging feature and is refining it, but plans to roll it out again in the coming months.
Without the facial-recognition tool, users can still manually tag their friends in pictures.
Rob Sherman, Facebook's manager of privacy and public policy, explained that the tool will only suggest a person who is a friend of the user uploading the picture.
He testified that third-parties, including the police, do not have access to the data Facebook uses for the feature.
"If people don't trust us, they won't use our service," Sherman said.
Sen. Richard Blumenthal (D-Conn.) pressed Sherman to commit that Facebook will never use its facial recognition tool on children younger than 13 years old.
Facebook is currently limited to people older than 13, but the company is considering providing a limited version of its site for young children.
Sherman emphasized that if Facebook does open up to young children, it will use strong privacy protections.
Franken also expressed concern during the hearing over a pilot program used by the FBI to compile people's facial images.
Jerome Pender, a deputy assistant director for the FBI, said the agency is only compiling criminal mugshots of people who have been arrested or imprisoned.
But the agency does scan people's faces to compare to its database for "criminal justice purposes."
Franken worried that if agents use the software to scan crowds at a protest, it could stifle free speech rights.
The Democratic senator showed images that he said the FBI had taken at political rallies, but Pender said he was unfamiliar with the pictures.
Franken said Congress should consider legislation to set clear guidelines for when police and private companies can scan and compile people's facial images.
"I fear that without further protections, this technology could be used on unsuspecting civilians innocent of any crime, or could be used to instantly identify someone walking down the street," he said. "I urge the FBI and Facebook to do more to protect people’s privacy so that this new technology isn’t abused."