Immigration and Nationality Act Section 287(g)

Section 287(g) of the U.S. Immigration and Nationality Act authorizes the Department of Homeland Security (DHS) to deputize selected state and local law enforcement officers to enforce federal immigration law. Section 287(g) allows the DHS and law enforcement agencies to make agreements, which require the state and local officers to receive training and work under the supervision of U.S. Immigration and Customs Enforcement.

Source: Wikipedia — Immigration and Nationality Act Section 287(g) (CC BY-SA 4.0)