A group of Democratic senators asked the Federal Communications Commission to investigate cell site simulators like Stingrays to determine if the surveillance devices used by local law enforcement agencies are disrupting cellphone service for ordinary consumers and 911 calls. The senators are also asking the FCC to look into whether Stingray use disproportionately affects people of color.

Cell site simulators, commonly known as IMSI catchers or by the brand name Stingray, pose as normal cellphone towers. When nearby phones connect, the simulators can capture their unique ID numbers, track their locations and intercept the contents of calls and messages. Law enforcement agencies tend to be secretive about their use of Stingrays, but several civil rights groups, including Center for Media Justice, ColorOfChange.org and New America’s Open Technology Institute, claimed in August that the Baltimore Police Department’s use of the devices was inhibiting emergency calls and unfairly targeting communities of color.

The organizations complained to the FCC, asking it to intervene. According to the complaint (PDF), BPD used Stingrays 4,700 times over the course of nine years to investigate everything from kidnappings to petty thefts. Because the devices affect any phone within a 200-500 meter radius, it could absorb not only a suspect’s calls but also calls to emergency services, suicide hotlines and other important resources. The complaint also cites USA Today reporting that shows BPD most commonly used Stingrays in black communities.

“We are particularly concerned about allegations that cell site simulators — commonly referred to as ‘Stingrays’ — disrupt cellular service and may interfere with calls for emergency assistance, and that the manner in which cell site simulators are used may disproportionately impact communities of color. While we appreciate law enforcement’s need to locate and track dangerous suspects, the use of Stingray devices should not come at the expense of innocent Americans’ privacy and safety, nor should law enforcement’s use of the devices disrupt ordinary consumers’ ability to communicate,” Senators Al Franken, Patrick Leahy, Ron Wyden, Sherrod Brown, Edward Markey, Elizabeth Warren, Jeff Merkley, Tammy Baldwin, Bernie Sanders, Tom Udall, Martin Heinrich and Chris Coons wrote in a letter to FCC Chairman Tom Wheeler.

The senators are asking the FCC to explain the cellphone interference caused by Stingrays and how the devices should be licensed and regulated.