Arizona v. United States (2012)
Background Information
Understanding the facts and constitutional questions
Connecting to Our Guiding Question
When, if ever, should the government be allowed to limit a person's constitutional rights in order to protect the community?
This case asks: When may a state write its own immigration rules, if the Constitution also gives that power to the federal government? This is a fight about federalism and the Supremacy Clause. It is about who has the authority to make these rules. It is not about whether immigration itself is good or bad.
Key People in This Case
Passed S.B. 1070. Arizona’s leaders argued that the federal government was not doing enough to enforce immigration law. One part of the law was about lawful police stops. It required police to check a person’s immigration status when they reasonably suspected the person was in the country without legal permission.
Sued Arizona before the law took effect. The federal government argued that immigration is a national responsibility and that Arizona’s law got in the way of federal immigration law.
Signed S.B. 1070 into law in April 2010. She defended the law as necessary to protect Arizona and its residents from the effects of people crossing the border without permission.
Organizations like the ACLU opposed the law. They argued it would lead to racial profiling, with police stopping Latino Americans because of how they look.
What Happened?
In April 2010, Arizona Governor Jan Brewer signed a law called S.B. 1070. Arizona’s leaders said the state was paying high costs for undocumented immigrants in schools, hospitals, and law enforcement. They also said the federal government was not doing enough to enforce immigration laws.
Four parts of the Arizona law were challenged in court. Section 3 made it a state crime to not carry federal immigration registration papers. Section 5(C) made it a state crime for a worker without federal permission to work in the United States to look for or do a job. Section 6 let police arrest someone without a warrant if they believed the person had done something that could get them deported, or removed from the country. Section 2(B) told police to check a person’s immigration status during a lawful stop, detention, or arrest. It applied when police reasonably suspected that the person was in the country unlawfully.
The law caused controversy right away. Civil rights organizations like the ACLU argued that it would lead to racial profiling of Latino Americans, who might be stopped because of how they looked. Protests took place across the country.
The federal government sued Arizona, arguing that the state law conflicted with federal immigration law. The government’s position was that immigration is a federal responsibility, not a state one.
The Big Question
Can states pass their own immigration laws? Or is immigration only the federal government’s responsibility?
What You Need to Know
The Supremacy Clause (Article VI, Clause 2) says:
"This Constitution, and the Laws of the United States which shall be made in Pursuance thereof...shall be the supreme Law of the Land...any Thing in the Constitution or Laws of any State to the Contrary notwithstanding."
This means that when federal law and state law conflict, federal law wins.
The Constitution also gives the federal government power over naturalization, the process of becoming a citizen, and over relations with other countries. Immigration involves relationships with other countries.
Important Facts
- Arizona borders Mexico, and many undocumented immigrants live there.
- Governor Jan Brewer signed S.B. 1070 into law in April 2010.
- People nicknamed S.B. 1070 the "show me your papers" law.
- Civil rights groups like the ACLU opposed the law because they feared racial profiling.
- Protests against the law took place across the country before it took effect.
- The federal government sued before the law took effect.
- The federal government has long been in charge of immigration.
- Arizona argued that the federal government was not doing enough.
Vocabulary
Argument Sorting Activity
Work with your group to sort these arguments
Instructions: For each argument, choose which side you would use it for — or “Both.” There is no score. The same fact can help opposite sides. Then rank and steelman in Weigh below.
The Two Sides
Arizona
States have the authority to protect the people who live in them. Arizona argues that states can step in to help when the federal government does not enforce immigration laws well enough. In Arizona’s view, its law only helps enforce federal law that already exists.
United States
The United States argues that immigration is a federal responsibility under the Supremacy Clause. It says states cannot create their own immigration policies, because those policies interfere with federal authority. They also create conflicting laws across the country.
| Argument | Answer |
|---|---|
| The Constitution gives the federal government broad power over immigration and naturalization. Evidence: Article I, Section 8 gives Congress power over "naturalization" (how people become citizens). The Supreme Court ruled in Chy Lung v. Freeman (1875) that immigration is a federal power because it involves foreign relations — something only the national government can handle. | |
| States have always helped enforce federal laws within their borders. Evidence: State and local police help enforce federal drug laws, bank robbery laws, and kidnapping laws. Under the 287(g) program, the federal government trains local officers to enforce immigration law. Arizona argued it was just helping — not replacing — federal enforcement. | |
| Federal immigration law is so complete that it leaves no room for state laws. Evidence: The Immigration and Nationality Act (INA) is a long, detailed federal law that covers every aspect of immigration: who can enter, how long they can stay, how to become a citizen, and what happens if they break the rules. There's no gap for states to fill. | |
| Arizona argued its law mostly matched federal rules instead of creating a new immigration system. Evidence: Federal law already requires non-citizens to carry registration documents, and Arizona's Section 3 made breaking that same rule a state crime. Arizona argued it was enforcing existing federal rules, not inventing new ones. (Section 5(C) was different: it made looking for work a state crime for undocumented workers, which federal law does not.) | |
| The federal government doesn't have enough resources to enforce immigration law everywhere. Evidence: In 2010, ICE (Immigration and Customs Enforcement), the agency that enforces immigration law inside the country, had about 20,000 employees nationwide, and Arizona's border with Mexico is about 372 miles long. Arizona argued the federal government could not cover all of it and that state police could help fill the gap. | |
| State immigration enforcement could interfere with America's relationships with other countries. Evidence: Mexico's government formally protested SB 1070. If each of the 50 states had different immigration policies, foreign countries wouldn't know who to negotiate with. The Constitution gives the federal government alone power over foreign affairs. | |
| Arizona faces special problems from illegal immigration because it borders Mexico. Evidence: Arizona shares a border of about 372 miles with Mexico. In 2010, the Pew Research Center estimated that about 400,000 undocumented immigrants lived in Arizona — about 6% of the state's population. Arizona argued that border states face challenges that states like Vermont or Maine don't. | |
| Different state immigration laws would create confusing and conflicting rules across the country. Evidence: If all 50 states made their own immigration rules, someone might be legal in California but illegal in Arizona. Immigrants wouldn't know which rules to follow. The United States argued the country needs one set of immigration rules for everyone. | |
| The Supremacy Clause makes federal law more important than conflicting state laws. Evidence: Article VI of the Constitution says federal law is "the supreme Law of the Land." When state and federal laws conflict, federal law wins. Lawyers call this "preemption" — the legal term for when federal law takes over an area and blocks state laws. | |
| States have the right to protect their borders and citizens from harm. Evidence: The 10th Amendment reserves powers to the states. States have "police powers" to protect public safety, health, and welfare. Arizona argued that protecting citizens from crime associated with illegal border crossings is a basic state responsibility. | |
| State enforcement of immigration law could lead to racial profiling and discrimination. Evidence: Critics called SB 1070 the "show me your papers" law. The ACLU warned that police might stop people just because they "look Latino." About 30% of Arizona's population is Hispanic — many are U.S. citizens or legal residents who could be unfairly targeted. | |
| In 2011, federal immigration officials told agents to focus on serious criminals and security threats, not on every undocumented immigrant. Evidence: In June 2011, ICE Director John Morton told agents to focus on national security, border security, and public safety, including serious criminals. The United States argued that Arizona's law would push officers to stop and hold people the federal government had chosen not to pursue, and that states can't override federal enforcement priorities. | |
| Arizona taxpayers pay high costs for illegal immigration in schools, hospitals, and police services. Evidence: The Federation for American Immigration Reform (FAIR), a group that favors less immigration, estimated that education, medical, and jail costs tied to illegal immigration were about $2.6 billion a year in Arizona. Arizona argued: if the federal government won't solve the problem, why should Arizona taxpayers pay the price? |
Key Terms for Arguments
Important concepts to understand when debating this case
When federal law takes over an area of law, states may not make their own rules that conflict with it. If a state law conflicts with federal law, the state law is “preempted” and cannot be enforced.
Evidence Vault
Real sources to build your debate arguments
Complete the Argument Sort to Unlock
Finish the Argument Sort above, then open the Evidence Vault for real case sources.
Analyze the Sources
Read each excerpt carefully. Decide which side of the case it supports — or if it could be used by both sides.
Border Security Crisis
Border Security Crisis
Cooperative Federalism
Cooperative Federalism
State Police Powers
State Police Powers
Public Safety Concerns
Public Safety Concerns
Federal Preemption Doctrine
Federal Preemption Doctrine
Foreign Policy Interference
Foreign Policy Interference
Discrimination and Harassment
Discrimination and Harassment
Frustration of Federal Discretion
Frustration of Federal Discretion
Connecting to Today
How these constitutional questions still matter
The tension between federal and state power did not end with this case. Consider these examples:
Sanctuary Cities
Some cities and states limit how much their police help federal immigration agents. Supporters call these "sanctuary" policies. In 2025, the Justice Department sued several of them, including Illinois, Chicago, and New York City. It argued that the policies get in the way of federal immigration enforcement.
Think about: If states can't make immigration stricter, can cities make it more lenient?
Marijuana Legalization
As of April 2026, 24 states had legalized marijuana for adults. It was still illegal under federal law, even after the federal government eased its rules for state-licensed medical marijuana that month. This creates a conflict between state and federal power, much like the conflict in the Arizona case.
Think about: When state and federal law conflict, which should win? Does it depend on the issue?
Border Security
Some border states have argued that they should have more power to enforce immigration laws. In December 2023, Texas passed S.B. 4. It made it a state crime to enter Texas from another country except at a legal port of entry. As of June 2026, a federal appeals court had allowed Texas to enforce the law while lawsuits continued.
Think about: Should states most affected by an issue have more say in how to handle it?
Discussion Questions
- Why might the Founders have given the federal government power over immigration and foreign relations?
- What problems could arise if each state had completely different immigration rules?
- Is there a way for states to address local concerns without conflicting with federal law?
Additional Resources
Go deeper with these resources