Preemption is the idea that when a federal law has been passed, state laws in violation of the federal law are deemed unconstitutional.

Arizona v. United States

567 U.S. 387 (2012).


Does the federal law preempt the Arizona law?


“Where Congress occupies an entire field . . . even complementary state regulation is impermissible.”

“State law is preempted where it ‘stands as an obstacle to the accomplishment and execution of the full purposes and objectives of Congress.”


The state law is preempted and thus unconstitutional.


Arizona passed a law which made it a misdemeanor to comply with federal alien-registration requirements. Additionally, the law made it a misdemeanor for unauthorized aliens to seek or engage in work in Arizona. As such, the United States sought to declare the law unconstitutional because it violated a federal law already in force.


Section 3 of the state law adds a state law penalty for conduct that is defined under federal law. However, because of the first rule stated above, even complementary functions are preempted. As such, the 3rd section fails.

Sections 5 of the state law is a bit more complicated. Here, the state law makes it a misdemeanor against “employees” instead of targeting the “employers.” The federal law had an express preemptive clause that prevented states from passing criminal laws against employers. As such, the state attempted to pass criminal laws against employees. According to the majority, the omission does not mean that there is no preemption. Instead, the court infers that congress did not intend there to be regulation against employees and thus the state law is preempted.

The dissents on the other hand focus on three principles:

  1. Scalia focuses on state sovereignty.
  2. Thomas focuses on the text of the Constitution. He says that the focus should be on the actual legislation, not on inferences of legislative intent.
  3. Alito says that inferences could be made in either direction. Congress could have omitted the preemption in the federal law on purpose, or it might not have done so. As such, the default is to rely on the text instead of the intent because there is no clear and manifest intent present.
Additional Notes

These were two new laws that were designed to help the federal government do their job, that is address issues at the southern border. Thus, the question turns to, can the states do so? The answer is no, why?

Here, the state is trying to adjust federal law. Something the state does not have the authority to do. In other words, Arizona is preempted by federal law.

There are three kinds of preemption:

  1. Occupy the fields preemption (the issue with Section 3, the federal covers ALL law within the field)
  2. Express preemption (the federal law says that there can be no state law on the matter)
  3. Conflict preemption (when there is a conflict in the federal law and the state law, the federal law wins; the issue with Section 5).


The content contained in this article may contain inaccuracies and is not intended to reflect the opinions, views, beliefs, or practices of any academic professor or publication. Instead, this content is a reflection on the author’s understanding of the law and legal practices.

Will Laursen

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