Iowa Code § 321.250: Equitable reprisal.

When the local authorities of other states shall, by the adoption of rules and regulations or otherwise, prohibit motor vehicles registered under the laws of this state from operating upon highways in any subdivision of such other state, the local authorities of this state may, by ordinance or otherwise, require the motor vehicles of the subdivisions of such other state while operating by their own power in this state to be registered under the laws of this state.