Arizona v. United States
The Supreme Court struck down three parts of Arizona's tough immigration law, ruling that making it a state crime to be an unregistered alien, to seek work without authorization, or to arrest people based only on suspected removability all interfered with the federal government's control over immigration.
But the Court let stand, for now, the law's requirement that police check the immigration status of people they lawfully stop, holding that Arizona courts should get a chance to interpret that provision before it is struck down as unconstitutional.
“Immigration policy shapes the destiny of the Nation.”
The majority's closing reflection on why federal control over immigration policy matters.
How it got here: A federal trial court blocked four provisions of Arizona's law before enforcement; the Ninth Circuit affirmed; Arizona asked the Supreme Court to review.
The Case in Depth
What happened
Arizona passed S.B. 1070 in 2010 to address the large number of unauthorized immigrants in the state, creating new state crimes for failing to carry alien registration papers and for unauthorized immigrants seeking work, giving police new arrest power over suspected removable immigrants, and requiring status checks during certain stops. The federal government sued to block the law, arguing it interfered with the federal immigration system.
The question before the Court
Could Arizona enforce its own state-law immigration crimes and arrest rules, like S.B. 1070, alongside the federal government's immigration system?
Why it matters
States that want to write their own immigration enforcement laws now know they largely cannot criminalize conduct the federal government already regulates or hand police broader arrest powers than federal officers have. At the same time, police in Arizona and states with similar laws can still ask about immigration status during lawful stops, at least until courts see how that plays out in practice.
What changes now
The case returns to the lower courts, with three of the four challenged provisions permanently blocked as preempted. The status-check provision can go into effect, but the Court left open the door for future legal challenges—including constitutional claims—once Arizona courts interpret the provision and it is applied in practice. Other states with similar immigration laws will likely see their own laws tested against this ruling.
What this does not decide
The Court did not decide whether the status-check provision is constitutional or whether it will cause unlawfully prolonged detentions in practice. It expressly left open future preemption and constitutional challenges to that provision once Arizona courts interpret it and it is actually enforced.
Concurrences and dissents
Dissent in part — Justice Scalia
“Neither the Constitution itself nor even any law passed by Congress supports this result. I dissent.”Scalia's opening statement rejecting the majority's preemption ruling as unsupported.
Justice Scalia argued that states retain an inherent sovereign power to exclude people from their territory that the Constitution never took away, and that none of Arizona's four provisions should be preempted. He would have upheld all of them, arguing the majority's reliance on field preemption improperly strips states of core sovereign authority, especially given lax federal enforcement.
Dissent in part — Justice Thomas
Justice Thomas would have upheld all four provisions because, in his view, none of them actually conflicts with the ordinary meaning of federal law. He rejected the majority's reliance on inferred congressional 'purposes and objectives,' arguing preemption should turn only on the text of federal statutes, not judicially guessed intentions.
Concurrence in part — Justice Alito
Justice Alito agreed with the majority that the status-check provision and the alien-registration crime were not problematic (agreeing the registration provision was preempted under Hines, and the status checks were not preempted). But he dissented on the work-authorization crime and the arrest provision, arguing both were consistent with existing precedent and added little to police authority already recognized under federal law.
How the Court got there
The legal reasoning, step by step
- The Court applied preemption principles under the Supremacy Clause, which lets federal law override conflicting state law. It explained two kinds of implied preemption: field preemption, where Congress has taken over an entire area so thoroughly that states cannot regulate it at all, and conflict preemption, where a state law stands as an obstacle to Congress's goals even without an outright contradiction.
- For the state crime of failing to carry alien registration papers, the Court found Congress had built a complete, all-embracing national registration system going back to a 1940s law, leaving no room for states to add their own registration crimes—so this was a field-preemption problem.
- For the state crime punishing unauthorized immigrants who sought work, the Court examined the federal Immigration Reform and Control Act and concluded that Congress deliberately chose to punish employers, not workers, with criminal penalties—making a state law criminalizing the worker's side an obstacle to that congressional choice, a conflict-preemption problem.
- For the provision letting local police arrest people based on suspected removability, the Court compared it to the narrower arrest authority Congress gave trained federal immigration officers and found the state provision gave police more unilateral power than the federal system allows, again standing as an obstacle to the federal scheme.
- For the status-check provision, the Court concluded there was no necessary conflict with federal law, since Congress has encouraged information-sharing between local police and federal immigration authorities, and any risk of unconstitutionally prolonged detentions was speculative until Arizona courts interpreted how the provision would actually operate.
Doctrinal impact
Cases affected by this decision
Reaffirms Hines v. Davidowitz (312 U. S. 52)
The Court relied on this 1941 ruling to hold that federal alien-registration law leaves no room for state registration crimes.
Limits De Canas v. Bica (424 U. S. 351)
The Court said this 1976 ruling upholding state employment laws no longer controls now that Congress has passed a comprehensive employer-sanctions law.