Verizon Communications, AT&T and Sprint will stop selling data on the locations of their wireless phone customers to external agencies.

The development follows accusations that one of the firms mishandled the information on the locations of the mobile phone customers.

The carriers said they will wind down data-sharing agreements with LocationSmart and Zumigo, which buy access to the real-time locations of users from major U.S. carriers and allow other businesses to tap into it, Wall Street Journal reported.

A Reuters report said an investigation by a U.S. Senator found law enforcement agencies were able to use the data to track people without their consent.

Consumers and lawmakers are increasingly concerned about privacy and security amid data breaches by tech firms, including Facebook.

In a letter to Senator Ron Wyden of Oregon dated June 15 and released by Wyden’s office on Tuesday, Verizon said it was beginning the process to stop selling customer location data to vendors that aggregate the data.

Wyden contacted the major carriers after his probe found that a prison phone company called Securus Technologies with access to such data had allowed law enforcement to use it to track people.

A Securus spokesman said the company was authorized to give law enforcement the location of a phone in certain circumstances, under Securus’ contract with the third party data aggregator.