WASHINGTON (AP) — Israel expects its top ally, the United States, to announce as soon as Monday that it’s blocking military aid to an Israeli army unit over gross human rights abuses in the Israeli-occupied West Bank before the war in Gaza began six months ago.

The move would mark the first time in the decades-long partnership between the two countries that a U.S. administration has invoked a landmark 27-year-old congressional act known as the Leahy law against an Israeli military unit.

It comes as the U.S.-Israeli relationship is under growing strain over civilian deaths and suffering in Israel’s war against Hamas in Gaza.

Here’s a look at the Leahy law and how it could be invoked:

WHAT IS THE LEAHY LAW?

Former Vermont Sen. Patrick Leahy championed legislation that became the Leahy law in the 1990s, saying the U.S. needed a tool to block American military aid and training to foreign security units guilty of extrajudicial killings, rapes, torture and other flagrant human rights abuses.