In the case of Lewis, Comptroller of Florida v. BT Investment Managers, Inc., et al., 1979, the U.S Supreme Court ruled on a Florida statute that prohibited out-of-state banks from owning or controlling businesses in Florida that provided investment advisory services. The court held that this law did not violate the Commerce Clause of the Constitution because it was designed to prevent economic concentration and conflicts of interest within financial institutions rather than discriminate against interstate commerce. However, they also found that it violated the Equal Protection Clause as there was no rational basis for discriminating between in-state and out-of-state banks when both could potentially cause similar harm to state interests. Therefore, while upholding part of its constitutionality under one clause, they struck down another aspect due to violation under a different constitutional provision.

In the dissenting opinion for Lewis v. BT Investment Managers, Inc., Justice William Rehnquist argued that Florida's law prohibiting out-of-state banks from owning or controlling businesses engaged in investment advisory activities within the state did not violate the Commerce Clause of the Constitution. He contended that states have a legitimate interest in regulating their own economic affairs and maintaining control over local industries, including banking and finance. Furthermore, he asserted that this case was different from previous cases where discriminatory laws were struck down because they served no purpose other than to economically isolate a state from its neighbors; here, there was an evident public policy rationale behind Florida’s decision to regulate foreign bank involvement in local investment firms - namely preventing undue concentration of economic power and preserving competition among financial institutions within its borders. Thus, according to Justice Rehnquist's view, it is not up to federal courts but rather each individual state legislature to decide whether such regulations are necessary or beneficial for their respective economies.