The reports showed that the number of requests for cellphone data are on the rise.
The wireless carriers said they provided some of the data in response to legal warrants, but that they also complied with many informal requests if the police said it was an emergency.
In Monday's letter, the Democrats also noted that the carriers acknowledged that they often accept payments for processing the police requests. Verizon, for example, charged police $50 to retrieve five days of text messages and $1,825 for multiple wiretap switches. AT&T received more than $8.2 million in 2011 for complying with the requests.
The wireless companies said that compensation is inconsistent and complying with requests often imposes costs on the companies. They insisted that they are not "selling" their customers' information to police.
The Democrats said the information provided by the carriers "raises concerns about law enforcement’s use of cell phone tracking and what is being done to protect the privacy of consumers."
A spokeswoman for the committee Republicans did not immediately respond to a request to comment.