An Arizona statute known as S. B. 1070 was enacted in 2010 to address pressing issues related to the large number of unlawful aliens in the State. The United States sought to enjoin the law as pre-empted. The
District Court issued a preliminary injunction preventing four of its provisions from taking effect. Section 3 makes failure to comply with federal alien-registration requirements a state misdemeanor; § 5(C) makes it a misdemeanor for an unauthorized alien to seek or engage in work in the State; § 6 authorizes state and local officers to arrest without a warrant a person “the officer has probable cause to believe . . . has committed any public offense that makes the person removable from the United States”; and § 2(B) requires officers conducting a stop, detention, or arrest to make efforts, in some circumstances, to verify the person’s immigration status with the Federal Government. The Ninth Circuit affirmed, agreeing that the United States had established a likelihood of success on its pre-emption claims.
Held:
1. The Federal Government’s broad, undoubted power over immigration and alien status rests, in part, on its constitutional power to “establish an uniform Rule of Naturalization,” Art. I, § 8, cl. 4, and on its inherent sovereign power to control and conduct foreign relations, see Toll v. Moreno, 458 U. S. 1, 10. Federal governance is extensive andcomplex. Among other things, federal law specifies categories of aliens who are ineligible to be admitted to the United States, 8 U. S. C. § 1182; requires aliens to register with the Federal Government and to carry proof of status, §§ 1304(e), 1306(a); imposes sanctions on employers who hire unauthorized workers, § 1324a; and specifies which aliens may be removed and the procedures for doing so, see § 1227. Removal is a civil matter, and one of its principal features is the broad discretion exercised by immigration officials, who must decide whether to pursue removal at all. Immigration and Customs Enforcement (ICE), an agency within the Department of Homeland Security, is responsible for identifying, apprehending, and removing illegal aliens. It also operates the Law Enforcement Support Center, which provides immigration status information to federal, state, and local officials around the clock.
Pp. 394–398.

