A previously unreleased Army study found that electric-shock gloves purchased by Immigration and Customs Enforcement caused intense pain and led military personnel posing as prisoners to stop resisting almost immediately.

ICE signed a $16.7 million contract in August to purchase 6,000 pairs of the gloves, despite agency officials being aware of the Army study’s findings.

The study found that participants experienced fatigue, soreness and fear of being shocked again, with some saying simply seeing the gloves afterward made them want to comply.

ICE describes the devices as tools intended to help officers quickly control detainees and protesters while reducing the need for more dangerous forms of force, CBS News has reported.

Critics are raising safety and oversight concerns because the gloves can deliver painful shocks without leaving visible marks, while ICE has not yet provided detailed answers about how the devices will be deployed and what training agents will receive.