A group of U.S. senators is pushing the Food and Drug Administration to finalize a ban on devices used to administer electric shocks to those with developmental disabilities in an effort to modify their behavior.

Six senators wrote to FDA Commissioner Robert Califf late last month asking the agency to cement a proposal that would prohibit electrical stimulation devices used for self-injurious or aggressive behavior.

“Put simply, it is outrageous that this practice is allowed in the United States for this vulnerable population and it should be stopped immediately. As such, we urge you to finalize the proposed rule as quickly as possible,” reads the letter signed by U.S. Sens. Chris Murphy, D-Conn., Tammy Baldwin, D-Wis., Richard Blumenthal, D-Conn., Cory Booker, D-N.J., Bob Casey, D-Pa., and Al Franken, D-Minn.

Earlier this year, the FDA proposed a ban on the devices which use electrodes attached to the skin to deliver electric shocks in order to condition individuals not to engage in certain behaviors. However, the agency has yet to move forward with issuing a final rule.

The devices are only known to be used at one facility in the nation — the Judge Rotenberg Educational Center in Canton, Mass., which serves children and adults with developmental disabilities as well as those with behavioral and emotional problems.

The Rotenberg Center has contended that the method offers a last resort for individuals with “life-threatening behavior disorders,” but disability advocates have largely aligned against the approach calling it harmful and ineffective.

In proposing to bar the devices, the FDA said it “determined that these devices present an unreasonable and substantial risk of illness or injury that cannot be corrected or eliminated by labeling.”

FDA spokeswoman Deborah Kotz said that the agency has received the senators’ letter and plans to respond to the lawmakers directly. At present, the FDA is still reviewing public comments submitted in response to the proposal, she said.