A group of U.S. senators led by Democrat Catherine Cortez Masto of Nevada urged Immigration and Customs Enforcement to cancel its plan to outfit officers with gloves that can deliver painful electric shocks.

In a letter to ICE’s acting director Thursday, Cortez Masto and 15 of her colleagues in the Democratic caucus questioned ICE’s need to spend up to $20 million to buy the devices, as well as the agency’s ability to use them appropriately.

“The blatant and tragic misuse of force in Los Angeles, Chicago, Minneapolis, Houston, Maine, and other locations around the country raises significant skepticism about the agency’s professional capability to safely deploy a new tool that could be used to harm Americans without cause,” the letter said.

In addition to Cortez Masto, the letter was signed by Independent Sen. Angus King of Maine and 14 other Democrats, who are in the minority in the Republican-controlled Senate. They are the latest to express opposition to the plan, which became public this month when ICE published a notice outlining plans to purchase thousands of “conductive distraction and de-escalation devices” for officers and investigators.

The devices are normal patrol gloves until an officer presses a button to activate the electrical mode. They must be applied directly to someone’s skin to produce a shock that causes pain, which is promoted as a way to gain compliance from people who are resisting. They have been used by some local jails and police departments in recent years.

Cortez Masto and the other senators said the device “presents substantial risks if deployed during civil arrests — even more so if it is deployed without clear limits, appropriate training, and comprehensive oversight.” They said that if ICE moves forward with the plan, it must make public details about how officers will be trained and how the use of the gloves will be documented and reviewed internally to avoid misuse.

White House border czar Tom Homan has argued that the gloves could be another way to gain compliance without resorting to the use of deadly force and could be particularly effective in detention settings. He has said that it will be months before they are deployed because the agency is working out training and policy details.

Ryan J. Foley, The Associated Press