According to ProPublica, it’s commonly done using Leahy Laws:
The recommendations came from a special committee of State Department officials known as the Israel Leahy Vetting Forum. The panel, made up of Middle East and human rights experts, is named for former Sen. Patrick Leahy, D-Vt., the chief author of 1997 laws that requires the U.S. to cut off assistance to any foreign military or law enforcement units — from battalions of soldiers to police stations — that are credibly accused of flagrant human rights violations.
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Over the years, hundreds of foreign units, including from Mexico, Colombia and Cambodia, have been blocked from receiving any new aid. Officials say enforcing the Leahy Laws can be a strong deterrent against human rights abuses.