In the case of Maryland et al. v. Louisiana, the Supreme Court ruled against a Louisiana law that imposed a tax on natural gas transported from federal offshore areas through pipelines crossing Louisiana to other states. The court held that this law violated both the Supremacy Clause and Commerce Clause of the U.S Constitution. The Supremacy Clause establishes federal laws as supreme over state laws when they conflict, while the Commerce Clause gives Congress exclusive authority over interstate commerce. In its decision, the court reasoned that by taxing federally owned resources in transit across state lines, Louisiana was effectively interfering with federal control over these resources and obstructing interstate commerce.

In the dissenting opinion for Maryland et al. v. Louisiana, Justice Rehnquist disagreed with the majority's decision to strike down Louisiana's tax on natural gas as unconstitutional under the Commerce Clause and Supremacy Clause of the U.S. Constitution. He argued that states should have more authority in regulating their own resources, especially when it comes to taxation policies which are traditionally within a state’s purview. Furthermore, he contended that there was no clear evidence showing this particular tax had an adverse effect on interstate commerce or conflicted with federal law or policy regarding energy regulation; hence, it did not violate either clause according to him. The justice also expressed concern about potential implications of this ruling on other similar state taxes and regulations.