In the case of Hillsborough County, Florida, et al. v. Automated Medical Laboratories, Inc., 1984, the U.S Supreme Court ruled in favor of Automated Medical Laboratories (AML). The court held that a local ordinance enacted by Hillsborough County requiring all medical testing laboratories to be licensed and regulated was preempted by federal law under the Public Health Service Act. AML had been operating mobile blood-drawing units without complying with this ordinance and argued that it was already subject to extensive federal regulation which superseded any local laws or regulations. The Supreme Court agreed with AML's argument stating that when state law stands as an obstacle to accomplishing Congressional objectives expressed in Federal Law then it is preempted.

In the dissenting opinion for Hillsborough County, Florida v. Automated Medical Laboratories, Inc., Justice White argued that local health and safety regulations should not be preempted by federal law unless there is a clear conflict between the two. He believed that the majority's decision to strike down local blood plasma testing requirements because they were more stringent than federal standards was misguided. According to him, it undermined states' rights and their ability to protect public health as they see fit. Furthermore, he pointed out that Congress had not explicitly stated an intention to supersede state laws in this area when it enacted relevant legislation at the federal level. Therefore, he concluded that both levels of regulation could coexist without contradiction or conflict.