How do federal, state and local laws fit together?

#Three levels, three sets of laws

Congress can pass laws only on subjects the Constitution assigns to it, such as commerce among the states and naturalization. The Tenth Amendment says powers not given to the federal government, and not denied to the states, are reserved to the states or to the people. Counties, cities and towns are created under state law. They pass local laws, called ordinances, using powers the state gives them.

#What the Supremacy Clause says

Article VI makes three things “the supreme Law of the Land”: the Constitution, federal laws made under it, and treaties. Judges in every state must follow them over any conflicting state law. When a valid federal law displaces a state law, courts call it preemption. The Supreme Court recognizes three kinds.

• Express: Congress says so in the law.
• Field: Congress regulates an area so fully that it leaves no room for the states.
• Conflict: obeying both laws is impossible, or the state law blocks the federal law’s purposes.

#Limits on federal power over states

Supremacy does not let the federal government run state governments. Under the anticommandeering doctrine, Congress cannot give direct orders to state legislatures. It also cannot force states to enact and enforce a federal regulatory program. The Supreme Court restated this rule in Murphy v. National Collegiate Athletic Association (2018), relying on two earlier rulings, New York v. United States and Printz v. United States.

#Where local laws fit

Local governments have only the powers their state grants. In 1907 the Supreme Court described cities as “convenient agencies” for using powers the state entrusts to them. Each state decides how much freedom to give. In Pennsylvania, for example, a municipality with a home rule charter can use any power not denied by the state constitution, its charter or the General Assembly. The legislature can deny such powers at any time.

#Examples of overlap

• Immigration: In Arizona v. United States (2012), the Supreme Court ruled 5–3 that federal law preempted three parts of an Arizona immigration law, and it allowed a fourth to take effect. The opinion described federal power over immigration as “broad, undoubted power.”
• Driver’s licenses: States issue them. The REAL ID Act sets minimum security standards for licenses that federal agencies accept for official purposes, such as boarding a commercial flight. Enforcement began May 7, 2025, and agencies may phase it in until May 5, 2027.
• Crimes: One act can break both federal and state law. In Gamble v. United States (2019), the Supreme Court confirmed that both governments may prosecute it.