## Facts

- Arizona enacted S.B. 1070 to address the effects of unlawful immigration within the state.
- The United States sued Arizona, alleging that federal immigration law preempted key provisions of S.B. 1070 under the Supremacy Clause and sought a preliminary injunction.
- Four provisions were challenged:
  - § 3: created a state misdemeanor for failure to comply with federal alien-registration requirements.
  - § 5(C): created a state misdemeanor for unauthorized noncitizens to seek or engage in work.
  - § 6: authorized warrantless arrest if an officer had probable cause to believe a person committed an offense making the person removable.
  - § 2(B): required officers, during certain stops/detentions/arrests, to attempt to verify immigration status with the federal government when reasonable suspicion existed, and to determine status before release after arrest.

- The federal district court preliminarily enjoined enforcement of §§ 2(B), 3, 5(C), and 6; the Ninth Circuit affirmed.
- The Supreme Court granted certiorari to review the preliminary injunction.

## Issues

1. Whether federal immigration law preempts Arizona S.B. 1070 § 3 criminalizing violations of federal alien-registration requirements.
2. Whether federal immigration law preempts S.B. 1070 § 5(C) criminalizing unauthorized noncitizens who seek or perform work.
3. Whether federal immigration law preempts S.B. 1070 § 6 authorizing warrantless arrests based on removability.
4. Whether federal immigration law preempts S.B. 1070 § 2(B) requiring immigration-status verification during certain law-enforcement encounters.

## Decision

- The Court affirmed in part and reversed in part the preliminary injunction.
- § 3 was preempted because Congress occupied the field of alien registration.
- § 5(C) was preempted because it conflicted with Congress’s chosen balance in regulating unauthorized employment.
- § 6 was preempted because it conflicted with the federal system governing immigration arrests and removals and interfered with federal enforcement discretion.
- § 2(B) was not preempted on its face at the preliminary-injunction stage; enjoining it was premature because it could be implemented in a way that avoids conflict with federal law.
- The Court left open future as-applied challenges to § 2(B), including if enforcement results in detention being prolonged solely to complete status checks or otherwise creates conflicts.

## Legal Principles

- Under the Supremacy Clause, state law is preempted where Congress occupies an entire field (field preemption) or where state law conflicts with federal law by obstructing federal objectives (obstacle/conflict preemption).
- The federal government has primary authority over immigration and noncitizen status, tied to the naturalization power and national control over foreign relations.
- When Congress creates a comprehensive registration system for noncitizens, states may not impose parallel or additional criminal penalties in that field.
- Where Congress selects specific enforcement mechanisms and penalties within a federal regulatory scheme (such as employer-focused sanctions for unauthorized employment), a state may not reconfigure that scheme by imposing additional criminal liability that Congress chose not to impose.
- State arrest authority in the immigration context is limited by the federal statutory framework and by the Executive Branch’s discretion in removal and enforcement priorities; state laws that expand arrest authority in ways that interfere with that framework may be preempted.
- State-federal information sharing regarding immigration status is generally permitted; facial preemption is inappropriate where a statute can reasonably be read and implemented to avoid conflict, though unconstitutional or conflicting applications remain subject to later litigation.

## Conclusion

The Court held that federal immigration law preempted Arizona’s state crimes for alien-registration violations and unauthorized work, and Arizona’s warrantless-arrest provision tied to removability, but allowed the immigration-status verification requirement to take effect because its operation could be consistent with federal law, subject to later as-applied challenges.


Arizona v. United States, 567 U.S. 387 (2012)