A city passes an ordinance and a state legislature nullifies it. This happens regularly across the United States, and it follows from where municipal authority comes from in the first place.
Cities are creatures of the state
Municipal governments in the United States have no independent constitutional standing. Their powers are granted by the state, and what a state grants it can generally withdraw.
This principle, long established in American law, means a city ordinance exists only within the space state law leaves for it.
Preemption is therefore not an unusual intervention but the ordinary operation of the hierarchy between the two levels of government.
Home rule provides partial protection
Many states grant home rule authority, allowing municipalities to legislate on local matters without seeking specific permission for each subject.
The protection is limited, since home rule generally yields where the state has legislated on the same subject or declared the matter one of statewide concern.
How far home rule extends differs substantially between states, which is why identical ordinances survive in one state and fall in another.
Preemption can be express or implied
Express preemption occurs where a statute states directly that local regulation of a subject is prohibited, leaving little room for argument.
Implied preemption is inferred from a statutory scheme comprehensive enough that the legislature is taken to have occupied the field.
Litigation over the second kind is common, because whether a scheme is comprehensive is a matter of interpretation rather than of text.
Punitive provisions raise the stakes
Some preemption statutes go beyond invalidating ordinances and attach consequences, including withholding state funds or exposing officials to personal liability.
These provisions change local behaviour before any litigation occurs, since a city may decline to legislate rather than risk the penalty.
They are also the most contested, as they reach beyond the ordinance itself to the conduct of local officials.
The pattern follows urban and state divergence
Preemption disputes concentrate where large cities and their state legislatures reach different policy conclusions on the same questions.
Because urban populations often differ demographically from statewide electorates, the divergence is structural rather than occasional.
The specific rules governing municipal authority vary by state and change with legislation, so the position in any particular place is a question of that state's current law.