https://www.wired.com/story/fcc-fines-wireless-companies-selling-users-location-data/

In May 2018, The New York Times reported that a company called Securus had sold law enforcement agencies access to the locations of people’s cellphones. Police were supposed to provide a warrant or other documentation proving they had authority to see the data, but the Times said Securus often didn’t check.

Subsequent stories by ZDNet and Vice Motherboard revealed an industry of middlemen that acquired location information from AT&T, Sprint, T-Mobile, and Verizon and resold it to companies like Securus. Some of the information came from the bail bonds industry, raising concerns that stalkers could buy their victims' location information.