In 1965, Congress authorized states to collect fees for each vehicle operated by an interstate transportation company within state borders. Under its reciprocity policy, the State of Michigan (defendant) did not impose registration fees for vehicles registered in states that did not impose fees for Michigan-registered vehicles. As a result, Yellow Transportation, Inc. (Yellow Transportation) (plaintiff) was not required to pay Michigan registration fees for some of its trucks. Congress later passed the Intermodal Surface Transportation Efficiency Act of 1991 (ISTEA), 49 U.S.C. § 11506, with the goal of maintaining state revenue flows while reducing the burden on carriers. The ISTEA directed the Interstate Commerce Commission (ICC) to create a new single-state registration system that minimized costs of compliance by capping per-vehicle fees at the level that each state was charging as of November 15, 1991. To implement the ISTEA, the ICC promulgated regulations that required participating states to cap their fees at the level charged under existing reciprocity agreements. Thereafter, Michigan altered its reciprocity agreement, requiring Yellow Transportation to pay registration fees. Yellow Transportation brought suit against Michigan in the Michigan Court of Claims, arguing that Michigan’s collection of fees violated the ISTEA’s fee-cap provision. The court of claims ruled in Yellow Transportation’s favor, and the court of appeals affirmed. The Michigan Supreme Court reversed. The United States Supreme Court granted certiorari to determine whether Michigan was required to enforce the ICC’s interpretation of the ISTEA’s fee-cap provision.