Judicial branch · Landmark case
Arizona v. United States
567 U.S. 387 (2012) · Opinion of the Court
What you should know
This page explains the Court’s holding in plain language, where the official text lives, and what to check next.
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The Court held that three of the four challenged provisions of Arizona’s SB 1070 immigration law were preempted by federal law — states cannot create their own state-level immigration crimes or take enforcement actions that conflict with, or intrude on, the federal government’s exclusive authority over immigration. But the Court let stand the law’s most well-known provision: requiring police to check a person’s immigration status during a lawful stop when there’s reasonable suspicion the person is in the country unlawfully.
Background
Arizona passed SB 1070, the “Support Our Law Enforcement and Safe Neighborhoods Act,” establishing an official state policy of “attrition through enforcement” against unauthorized immigration. The federal government sued to block it, arguing the law intruded on the federal government’s exclusive constitutional authority over immigration. Four provisions were at issue: making it a state crime to violate federal alien-registration rules, making it a state crime for an unauthorized immigrant to seek work, authorizing warrantless arrests based on suspected removability, and requiring police to verify immigration status during lawful stops.
The Court struck down the first three as impermissibly stepping into a field the federal government occupies exclusively or as conflicting directly with federal enforcement priorities. It upheld the fourth — the status-check provision — on its face, while cautioning it could still face future challenges depending on how it was actually enforced in practice, including concerns about racial profiling.
A real test of how far states can go on immigration enforcement — with a split result.
Arizona became a template case for federal preemption doctrine in immigration: most state attempts to independently criminalize immigration status get struck down, but police status-checks during otherwise-lawful stops survive, at least on their face. Several other states with similar laws had to revise them after this ruling.
Vote and authorship
| Majority | Kennedy, J. (opinion of the Court) |
|---|---|
| Join | Roberts, C.J., Ginsburg, Breyer, Sotomayor |
| Concur/dissent | Scalia, J.; Thomas, J.; Alito, J. (each separately) |
| Not participating | Kagan, J. |
The Government of the United States has broad, undoubted power over the subject of immigration and the status of aliens.
Justice Kennedy · Arizona v. United States
How it fits in government
Executive branch
Immigration enforcement priorities and discretion sit primarily with federal agencies — this ruling protects that discretion from being overridden by state law.
Judicial branch
A significant modern application of federal preemption doctrine under the Supremacy Clause — when state and federal law conflict, or when federal law occupies a field entirely, state law must yield.
State & local government
States retain some room to cooperate with federal immigration enforcement, as this ruling’s treatment of the status-check provision shows, but cannot create parallel state immigration law.
Official records visitors may need
SupremeCourt.gov
Opinions, docket search, rules, and Court information.
Oyez
Case abstract, oral argument audio, and justice votes.
Opinion text (Justia)
Readable public text of the case.
GovInfo · U.S. Courts
Official publications and related federal court materials.
Related research paths
Supremacy Clause & preemption
The constitutional doctrine that federal law overrides conflicting state law.
Federal immigration agencies
How immigration enforcement is actually structured at the federal level.
State and local law enforcement cooperation
Where state and local police can and can’t assist with federal immigration enforcement.
Landmark cases guide
Other holdings that define federal-state power.