The U.S. Supreme Court case Wisconsin Public Intervenor, et al. v. Ralph Mortier, et al., 1990 revolved around the Federal Insecticide, Fungicide and Rodenticide Act (FIFRA). The State of Wisconsin had imposed additional restrictions on pesticide use beyond those set by FIFRA which were challenged as being pre-empted by federal law. However, the court ruled in favor of Wisconsin stating that nothing in FIFRA's language or legislative history suggested it was meant to be all-encompassing regulation that would prevent states from imposing further regulations if they saw fit for their specific circumstances. Therefore, local governments could impose stricter controls on pesticides than those required under federal law without violating the Supremacy Clause of the Constitution.

In the dissenting opinion for Wisconsin Public Intervenor v. Ralph Mortier, Justice Stevens argued that the majority's interpretation of Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) was incorrect. He believed that Congress intended to allow states to regulate pesticide use more strictly than federal law does if they choose to do so. However, he disagreed with the majority's view that this intent extended to allowing local governments such as counties or municipalities to enact their own regulations on top of state laws. According to Justice Stevens, there is no clear evidence in FIFRA’s text or legislative history indicating Congress meant for it also apply at a local level; rather its language suggests an intention for uniformity across each state regarding pesticide regulation under federal standards. Therefore, he concluded that county ordinances like those at issue in this case are preempted by FIFRA and thus invalid.