U.S. Sen. Al Franken on Wednesday wrote a letter to Apple CEO Tim Cook asking him to explain to the American public how the newest iPhone’s addition of “Face ID” technology-a facial recognition tool that allows users to unlock their phones or make purchases with their faces-will impact consumer privacy and security.

Apple unveiled the new smartphone on Tuesday, and it will allow users to unlock the home screen and make purchases by simply looking at the phone Screen. The senator has long raised questions about the rapid proliferation of facial recognition technologies.

Sen. Franken asked Apple a series of questions about the iPhone X’s Face ID system, including how users’ “faceprints” will be protected and safeguarded, if at any point that data will be shared or sold to marketers, and whether or not law enforcement will be able to access the Face ID database.

“I am writing to request more information on Face ID – Apple’s new facial recognition system and the core feature of the recently unveiled iPhone X,” wrote Sen. Franken.

“While details on the device and its reliance on facial recognition technology are still emerging, I am encouraged by the steps that Apple states it has taken to implement the system responsibly. However, substantial questions remain about how Face ID will impact iPhone users’ privacy and security, and whether the technology will perform equally well on different groups of people. To offer clarity to the millions of Americans who use your products, I ask that you provide more information on how the company has processed these issues internally, as well as any additional steps that it intends to take to protect its users.”

In 2014, the legislator successfully fought back against a new app-called NameTag- that let strangers get a person’s very personal information simply by looking at them with a modified Google Glass device.