Arizona v. United States, decided June 25, 2012, is the Supreme Court decision that set the limits on how far a state can go in policing immigration inside its own borders. By a 5–3 vote, with Justice Kennedy writing for the majority, the Court struck down three provisions of Arizona’s Senate Bill 1070 as preempted by federal law and left one standing. Out went the state penalties for missing federal registration papers, the state crime of seeking or performing unauthorized work, and the authority for officers to make warrantless arrests based on suspected deportability. What survived was Section 2(B), the requirement that officers check immigration status during lawful stops, and even that was left on a short leash.
The Four Provisions at Issue
Arizona passed SB 1070 in 2010 to make “attrition through enforcement” the official policy of every state and local agency in the state. The legislature said the provisions were “intended to work together to discourage and deter the unlawful entry and presence of aliens and economic activity by persons unlawfully present in the United States.”1Arizona Legislature. Arizona Senate Bill 1070 – Support Our Law Enforcement and Safe Neighborhoods Act The federal government challenged four sections before the law took effect.
Section 2(B) required officers to make a reasonable attempt to verify immigration status during any lawful stop, detention, or arrest when they had reasonable suspicion the person was in the country unlawfully, and required status confirmation before release for anyone arrested.1Arizona Legislature. Arizona Senate Bill 1070 – Support Our Law Enforcement and Safe Neighborhoods Act Section 3 made it a state misdemeanor to fail to carry or complete federal alien registration documents. Section 5(C) made it a state misdemeanor for an unauthorized person to apply for or perform work in Arizona. Section 6 let state and local officers arrest anyone without a warrant if they had probable cause to believe the person had committed an offense making them deportable.
Why Preemption Decided the Case
The entire ruling turned on federal preemption. Under the Supremacy Clause, federal law is “the supreme Law of the Land,” and state law that conflicts with it must yield.2Constitution Annotated. Article VI – Supreme Law Two forms of preemption did the work in Arizona. Field preemption applies where Congress has built a regulatory system so complete that no room remains for state supplementation. Conflict preemption applies where a state law stands as an obstacle to what Congress was trying to accomplish, even without a direct textual clash. Immigration touches both: Congress has enacted comprehensive registration and enforcement schemes, and immigration decisions bear on foreign relations, an area where the nation needs to speak with one voice.
Section 3: State Penalties for Registration Failures Struck Down
Federal law already requires noncitizens over eighteen to carry their registration documents, and failure to do so is a federal misdemeanor punishable by up to a $100 fine, thirty days in jail, or both.3Office of the Law Revision Counsel. 8 USC 1304 – Forms for Registration and Fingerprinting Section 3 added a state misdemeanor on top of that federal crime. The Court held it was field-preempted, writing that “Congress has occupied the field” of alien registration and that “even complementary state regulation is impermissible.” The majority tied the conclusion to Hines v. Davidowitz, the 1941 case that struck down a Pennsylvania registration statute because Congress meant its federal registration plan to be a “single integrated and all-embracing system.”4Justia. Arizona v. United States
Section 5(C): Criminalizing Unauthorized Work Struck Down
The Immigration Reform and Control Act of 1986 targeted unauthorized employment by penalizing employers who knowingly hire unauthorized workers, requiring work-eligibility verification, and imposing fines and criminal penalties on offending businesses.5U.S. Citizenship and Immigration Services. USCIS Policy Manual Volume 10 Part A Chapter 1 – Purpose and Background Congress deliberately chose not to criminalize the workers themselves. Section 5(C) did exactly that, making it a state crime for unauthorized individuals to seek or perform work. The Court found the provision stood “as an obstacle to the federal regulatory system,” noting that “Congress decided it would be inappropriate to impose criminal penalties on unauthorized employees.”4Justia. Arizona v. United States Even where a state pursues the same broad objective as Congress, a “conflict in technique can be fully as disruptive to the system Congress enacted as conflict in overt policy.”6Supreme Court. Arizona v. United States
Section 6: Warrantless Arrests for Suspected Deportability Struck Down
Section 6 gave state and local officers authority to arrest anyone without a warrant when they had probable cause to believe the person had committed a deportable offense. The Court struck it down because it let state officers make judgments federal law reserves to federal officials. Removal, the majority wrote, “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.”6Supreme Court. Arizona v. United States
The opinion spelled out why that discretion matters. Immigration enforcement involves “immediate human concerns.” An unauthorized worker supporting a family presents different equities than a smuggler. A case may turn on U.S.-born children, community ties, or military service. Some cases carry foreign-policy weight because the person’s home country is in civil war or engaged in political persecution. Letting state officers bypass that analysis by making arrests based on their own read of deportability “creates an obstacle to federal law” because decisions about who stays and who goes “touch on foreign relations and must be made with one voice.”6Supreme Court. Arizona v. United States
Section 2(B): The Status-Check Provision Upheld
The Court declined to strike down Section 2(B), the “show me your papers” requirement. The majority reasoned that it was “improper to enjoin §2(B) before state courts construed it and without some showing that its enforcement actually conflicts with federal law.” Federal law already encourages information-sharing between state and federal officials on immigration status, so requiring status checks did not automatically clash with federal policy.4Justia. Arizona v. United States
The Court flagged what could still go wrong. If Section 2(B) were read to require officers to “delay release of detainees for no reason other than to verify immigration status,” that “would raise constitutional concerns” and “would disrupt the federal framework.”4Justia. Arizona v. United States Because this was a facial challenge brought before the law had ever been enforced, the challengers had to show the provision was unconstitutional in every possible application, and the Court found that showing had not been made. As-applied challenges over prolonged detention or profiling remained available for future cases.
The Dissents
Three justices disagreed with parts of the majority opinion.
Justice Scalia wrote the sharpest dissent. He argued that Arizona was exercising a sovereign power that predated the Constitution, contending that “as a sovereign, Arizona has the inherent power to exclude persons from its territory, subject only to those limitations expressed in the Constitution or constitutionally imposed by Congress.” In his view, Arizona had not contradicted federal law but had simply chosen to enforce federal restrictions more vigorously than the federal government cared to. He closed: “If securing its territory in this fashion is not within the power of Arizona, we should cease referring to it as a sovereign State.”6Supreme Court. Arizona v. United States
Justice Thomas would have upheld all four provisions. He rejected “purposes and objectives” preemption analysis outright, arguing that the inquiry should focus on whether the plain texts of the state and federal statutes actually conflict rather than being “a freewheeling judicial inquiry into whether a state statute is in tension with federal objectives.”6Supreme Court. Arizona v. United States
Justice Alito took a middle path. He agreed that Section 3 was preempted and that Section 2(B) was not, but he would have upheld Sections 5(C) and 6. On the employment provision, he read Congress’s express preemption of state laws targeting employers, paired with its silence on laws targeting employees, as leaving that space open for states. On warrantless arrests, he argued that federal law already contemplates cooperation with state officers in “apprehension” and “detention” of noncitizens and that Section 6 added little to authority officers already had.6Supreme Court. Arizona v. United States
What the Ruling Still Controls
Arizona v. United States remains the primary precedent whenever a state tries to build its own immigration enforcement system alongside the federal one. In the years after the decision, courts applied its framework to invalidate similar provisions in laws enacted by Alabama, Georgia, South Carolina, and Indiana. The logic was direct: if Arizona could not create state-level immigration crimes that paralleled federal ones, neither could anyone else.
A new generation of state laws is now testing that precedent. Texas enacted Senate Bill 4 in 2023, making it a state crime to enter Texas outside a lawful port of entry and authorizing state judges to order removal. Arizona voters approved Proposition 314 in November 2024, and Florida signed its own version in February 2025. These states argue variously that they hold a sovereign right of self-defense under Article I, Section 10, and that field preemption cannot apply “when the federal executive branch has abandoned the very field it now purports to occupy.” Challengers respond that lower courts have “routinely held that state immigration crimes paralleling their federal counterparts are field preempted” under the Arizona framework.7Congress.gov. Federal Preemption and State Authority to Deter the Presence of Unauthorized Aliens Whether the current Supreme Court will revisit or narrow Arizona v. United States is among the most closely watched questions in immigration law.