By Brendan Sasso - 11/10/11 09:07 PM EST
The document on cellphone data, which the ACLU obtained through a Freedom of Information Act request from the Justice Department, also showed that the carriers retain data on phone calls and text messages. The Justice Department compiled the document to help police officers obtain evidence.
"Customers are already paying money for their mobile service; they should not be paying with their personal information too," the ACLU wrote.
The civil liberties group urged the wireless companies to explain to their customers what information they collect and to notify them if that information is breached or shared with a third party. The letter asks the companies to not store location data without customers' explicit permission.
The ACLU also urges the companies to notify customers when their data is shared with the police "whenever legally possible."
"As stewards of private data, you have a great responsibility to protect this information and safeguard our trust," the group wrote.
The ACLU set up an online petition for users to urge wireless companies to "respect the privacy of cellphone customers."
An AT&T spokesman said "customer privacy is a priority" at the company and pointed to an April letter to Reps. Joe Barton (R-Texas) and Edward Markey (D-Mass.) in which the company said "providing transparent notice to customers about our collection and use of personal information—including wireless location data—is fundamental to our privacy practices and to the trust our customers place in us."
Other wireless companies did not immediately return a request to comment on the letter.