"The question before the Court is whether federal law preempts and renders invalid four separate provisions of the state law. ... The issue is whether, under preemption principles, federal law permits Arizona to implement the state-law provisions in dispute. ... Section 3 of S. B. 1070 creates a new state misde-meanor. It forbids the “willful failure to complete or carry an alien registration document . . . in violation of 8 United States Code section 1304(e) or 1306(a).” Ariz. Rev. Stat. Ann. §11–1509(A) (West Supp. 2011). ... As it did in Hines, the Court now concludes that, with respect to the subject of alien registration, Congress intended to preclude States from “complement[ing] the federal law, or enforc[ing] additional or auxiliary regulations.” 312 U. S., at 66–67. Section 3 is preempted by federal law. ... §5(C) enacts a state criminal prohibition where no federal counterpart exists. The provision makes it a state misdemeanor for “an unauthorized alien to knowingly apply for work, solicit work in a public place or perform work as an employee or independent contractor” in Arizona. Ariz. Rev. Stat. Ann. §13–2928(C) (West Supp. 2011). ... Section 5(C) is preempted by federal law. [IRCA.] ... Section 6 of S. B. 1070 provides that a state officer, “without a warrant, may arrest a person if the officer has probable cause to believe . . . [the person] has committed any public offense that makes [him] removable from the United States.” Ariz. Rev. Stat. Ann. §13–3883(A)(5) (West Supp. 2011). ... Congress has put in place a system in which state officers may not make warrantless arrests of aliens based on possible removability except in specific, limited circumstances. By nonetheless authorizing state and local officers to engage in these enforcement activities as a general matter, §6 creates an obstacle to the full purposes and objectives of Congress. See Hines, 312 U. S., at 67. Section 6 is preempted by federal law. ... Section 2(B) of S. B. 1070 requires state officers to make a “reasonable attempt . . . to determine the immigration status” of any person they stop, detain, or arrest on some other legitimate basis if “reasonable suspicion exists that the person is an alien and is unlawfully present in the United States.” Ariz. Rev. Stat. Ann. §11–1051(B) (West 2012). ... At this stage, without the benefit of a definitive interpretation from the state courts, it would be inappropriate to assume §2(B) will be construed in a way that creates a conflict with federal law. ... As a result, the United States cannot prevail in its current challenge. ... This opinion does not foreclose other preemption and constitutional challenges to the law as interpreted and applied after it goes into effect." - Arizona v. U.S., June 25, 2012.