In the case of City of Philadelphia et al. v. New Jersey et al., 1977, the U.S. Supreme Court ruled that states cannot discriminate against other states' waste in an attempt to reduce environmental hazards within their own borders. The state of New Jersey had enacted a law prohibiting the importation of most solid or liquid waste originating outside its boundaries into its landfills as part of an effort to address local environmental concerns and limit landfill use for out-of-state garbage disposal needs. However, this was challenged by several entities including the city of Philadelphia who argued that it violated the Commerce Clause which prohibits discrimination against interstate commerce. The court agreed with these challengers, ruling in a 7-2 decision that while protecting health and environment is indeed a legitimate goal for any state government, discriminating against out-of-state waste does not serve this purpose since all wastes are equally harmful regardless where they come from; thus such laws were unconstitutional because they unfairly burdened other states' ability to dispose off their trash effectively amounting to economic protectionism.

In the dissenting opinion for City of Philadelphia et al. v. New Jersey et al., Justice Rehnquist disagreed with the majority's view that New Jersey's law banning out-of-state waste was discriminatory and violated the Commerce Clause of the Constitution. He argued that states should have a right to protect their environment, even if it means restricting commerce in some way, as long as they are not discriminating against other states without reason or acting protectionist in nature. He believed that this case did not involve "simple economic protectionism" but rather an effort by New Jersey to preserve its own resources and environment from potential harm caused by excessive landfill waste disposal within its borders. Furthermore, he contended that there is no clear evidence showing how much interstate commerce would be affected by such laws compared to intrastate commerce; thus, striking down these laws based on speculation seems unjustified.