49 CFR § 533.7 - Preemption.
(a) General. When an average fuel economy standard prescribed under this chapter is in effect, a State or a political subdivision of a State may not adopt or enforce a law or regulation related to fuel economy standards or average fuel economy standards for automobiles covered by an average fuel economy standard under this chapter.
(b) Requirements must be identical. When a requirement under section 32908 of title 49 of the United States Code is in effect, a State or a political subdivision of a State may adopt or enforce a law or regulation on disclosure of fuel economy or fuel operating costs for an automobile covered by section 32908 only if the law or regulation is identical to that requirement.
(c) State and political subdivision automobiles. A State or a political subdivision of a State may prescribe requirements for fuel economy for automobiles obtained for its own use.
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