FCC Chairwoman Jessica Rosenworcel wants more information from mobile carriers on their data practices.

While many consumers are beginning to pay attention to the privacy offered by their web browsers, email accounts, and the apps installed on their phones, few think about the risk their wireless carrier poses. Wireless carriers have access to customers’ geolocation data and can link that data to specific users.

Rosenworcel wants to know exactly how carries are using that data, as well as their safeguards and retention policies.

“Accordingly, given the highly sensitive nature of this data—especially when location data is combined with other types of data, the ways in which this data is stored and shared with third parties is of utmost importance to consumer safety and privacy,” wrote Rosenworcel to T-Mobile CEO Mike Sievert. “I kindly ask that T-Mobile respond to the following questions regarding T-Mobile and Metro by T-Mobile’s consumer data retention policies for geolocation data and its policies regarding sharing of that data with third parties. Accordingly, given the highly sensitive nature of this data—especially when location data is combined with other types of data, the ways in which this data is stored and shared with third parties is of utmost importance to consumer safety and privacy. I kindly ask that T-Mobile respond to the following questions regarding T-Mobile and Metro by T-Mobile’s consumer data retention policies for geolocation data and its policies regarding sharing of that data with third parties.”

Rosenworcel sent similar letters to AT&T, Best Buy Health, Charter, Comcast, Consumer Cellular, C-Spire, Dish Network, Google, H20 Wireless, Lycaobile, Mint Mobile, Red Pocket, U.S. Cellular, and Verizon.