## Facts

- Arizona enacted S.B. 1070 (as amended), stating a policy of “attrition through enforcement” in state and local government.
- The United States sued Arizona and its Governor, alleging the law was preempted by federal immigration law under the Supremacy Clause and sought preliminary injunctive relief.
- The district court preliminarily enjoined enforcement of four provisions:
  - Section 2(B): required immigration-status checks during lawful stops/detentions/arrests when reasonable suspicion of unlawful presence exists and required status determination before release after arrest.
  - Section 3: created a state misdemeanor for failing to comply with federal alien-registration requirements and for not carrying registration documents.
  - Section 5(C): created a state misdemeanor for unauthorized noncitizens to apply for, solicit, or perform work.
  - Section 6: authorized warrantless arrests based on probable cause that a person committed an offense making the person removable.
- Arizona appealed the injunction as to those four provisions; the United States did not appeal denial of broader relief.

## Issues

1. Whether the United States showed a likelihood of success that Sections 2(B), 3, 5(C), and 6 are preempted by federal immigration law under the Supremacy Clause.
2. Whether the district court abused its discretion in finding irreparable harm, balance of equities, and public interest supported preliminary injunctive relief.

## Decision

- The Ninth Circuit affirmed the preliminary injunction against Sections 2(B), 3, 5(C), and 6.
- The court held the United States was likely to succeed on the merits that each enjoined provision is preempted.
- The court held the United States showed likely irreparable harm from interference with federal immigration policy and foreign-relations interests.
- The court concluded the balance of equities and public interest supported preserving the status quo pending final adjudication.
- One judge concurred in part and dissented in part, disputing preemption as to aspects of Section 2(B).

## Legal Principles

- Federal immigration regulation may preempt state law through field preemption (Congress fully occupies a field) or conflict preemption (state law obstructs federal objectives or discretion).
- Alien registration is a field occupied by federal law; a state may not add state criminal penalties tied to compliance with federal registration requirements.
- Under IRCA, Congress created a comprehensive scheme focused primarily on employer sanctions and chose not to criminalize unauthorized employees’ seeking or performing work; state employee-targeted criminalization likely conflicts with that choice.
- Arrest and removal decisions involve federal discretion; state arrest authority premised on removability risks interfering with federal enforcement judgments and priorities.
- Even where federal law permits information sharing, mandatory state status-check and detention requirements may conflict with federal priorities and resource allocation if they predictably burden federal systems and constrain federal discretion.
- In Supremacy Clause litigation, threatened disruption of federal enforcement policy and foreign-relations interests can constitute irreparable harm supporting preliminary relief.

## Conclusion

The Ninth Circuit upheld a preliminary injunction blocking enforcement of four core S.B. 1070 provisions, concluding the United States was likely to prove they intruded into federally occupied areas or conflicted with Congress’s immigration framework and the federal executive’s enforcement discretion, and that interim relief was warranted to prevent interference with federal immigration policy.


United States v. Arizona, 641 F.3d 339 (9th Cir. 2011)