Amazon is once again in the spotlight over privacy, with lawmakers wanting to know what the company plans to do with customer palm prints.

Amazon rolled out palm print biometric scanning as a way for customers to pay without having to use their card. The technology is already in use in Amazon Go, Amazon Books and Amazon 4-star stores, as well as some Whole Food locations.

Lawmakers are concerned about the company’s plans, according to TechCrunch, writing a letter to Amazon CEO Andy Jassy to express those concerns. In particular, Senators Amy Klobuchar (D-MN), Bill Cassidy (R-LA) and Jon Ossoff (D-GA) questioned whether Amazon would use the biometric data in its advertising business.

“Amazon’s expansion of biometric data collection through Amazon One raises serious questions about Amazon’s plans for this data and its respect for user privacy, including about how Amazon may use the data for advertising and tracking purposes,” the Senators wrote.

Amazon already has access to a wealth of information from their e-commerce operations and cloud business. It’s easy to see why there would be concern about them also having access to biometric data, especially if they plan to use it for anything other than a convenience service for their customers.