Facts of the case
On April 23, 2010, the Arizona State Legislature passed S.B. 1070; Governor Jan Brewer signed the bill into law. On July 6, 2010, the United States sought to stop the enforcement of S.B. 1070 in federal district court before the law could take effect. The district court did not enjoin the entire act, but it did enjoin four provisions. The court enjoined provisions that (1) created a state-law crime for being unlawfully present in the United States, (2) created a state-law crime for working or seeking work while not authorized to do so, (3) required state and local officers to verify the citizenship or alien status of anyone who was lawfully arrested or detained, and (4) authorized warrantless arrests of aliens believed to be removable from the United States.
Arizona appealed the district court's decision to the U.S. Court of Appeals for the Ninth Circuit. The appellate court affirmed the district court's decision, holding that the United States had shown that federal law likely preempted: (a) the creation of a state-crime for violation of federal registration laws, (b) the creation of a state-crime for work by unauthorized aliens, (c) the requirement to verify citizenship of all detained persons, and (d) the authorization for police officers to effect warrantless arrests based on probable cause of removability from the United States. Arizona appealed the court's decision.
Do the federal immigration laws preclude Arizona's efforts at cooperative law enforcement and preempt the four provisions of S.B. 1070 on their face?