On June 25, 2012, the Supreme Court decided Arizona v. United States, No. 11-182, holding that three out of four challenged provisions of Arizona law relating to immigration were preempted by federal law.

In 2010, the State of Arizona enacted a statute called the Support Our Law Enforcement and Safe Neighborhoods Act, known informally by its state senate bill number, S. B. 1070. Before the statute took effect, the United States filed suit to enjoin four of its provisions:

  • Section 3, which makes it a state misdemeanor for an alien to willfully fail to complete or carry an alien registration document;
  • Section 5(C), which makes it a state misdemeanor for an unauthorized alien to seek or perform work;
  • Section 6, which authorizes the arrest without warrant of any person that a state officer has probable cause to believe committed a public offense making the person removable from the United States; and
  • Section 2(B), which requires state officers to make a reasonable attempt to determine the immigration status of any person who is stopped or detained, and to actually determine the status of any person who is arrested before the person is released.

Both the United States District Court for the District of Arizona and the Ninth Circuit issued injunctions barring all four provisions from taking effect.

The Supreme Court affirmed the injunction as to the first three challenged provisions, but reversed as to the fourth.

Beginning with § 3, the Court held that "the Federal Government has occupied the [entire] field of alien registration," thus preempting all state regulation in that field—even laws that, like Arizona's, simply add state penalties to existing federal violations without changing the requirements.

Turning to § 5(C), the Court found Arizona's imposition of criminal penalties on unauthorized aliens for seeking or performing work to be preempted by the Immigration Reform and Control Act of 1986 (IRCA). IRCA imposes criminal penalties on employers but not on the unauthorized aliens who are employees. The Court was convinced that "IRCA's framework reflects a considered judgment that making criminals out of aliens engaged in unauthorized work—aliens who already face the possibility of employer exploitation because of their removal status—would be inconsistent with federal policy and objections." Thus, even though IRCA's express preemption provision did not apply to the Arizona statute, the Court found it preempted under conflict preemption principles because it stood as an obstacle to the accomplishment of federal purposes.

Regarding § 6, the Court found that it "attempts to provide state officers even greater authority to arrest aliens on the basis of possible removability than Congress has given to trained federal immigration officers." This would violate the principle that "[d]ecisions of this nature touch on foreign relations and must be made with one voice."

Finally, however, the provisions of § 2(B) regarding state officials' duties to confirm the immigration status of detainees or arrestees could not be held preempted before taking effect. Congress has required the department of Immigration and Customs Enforcement to respond to any request made by state officials for verification of a person's immigration status. 8 U.S.C. § 1373(c). And it "has done nothing to suggest it is inappropriate" for state officials to communicate with ICE in the circumstances required by Arizona. "The federal scheme thus leaves room for a policy requiring state officials to contact ICE as a routine matter."  The Court noted, however, that its "opinion does not foreclose other preemption and constitutional challenges to [section 2(B)] as interpreted and applied after it goes into effect."

Justice Kennedy delivered the opinion of the Court, in which Chief Justice Roberts and Justices Ginsburg, Breyer, and Sotomayor joined. Justices Scalia, Thomas, and Alito each filed opinions concurring in part and dissenting in part. Justice Kagan took no part in considering or deciding the case.

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