In the case of Pennsylvania v. Nelson, 1955, the U.S. Supreme Court ruled that state laws regarding sedition (conduct or speech inciting people to rebel against authority) were superseded by federal law and thus invalid. The court held in a 6-2 decision that Steve Nelson's conviction under Pennsylvania's Sedition Act was unconstitutional because it conflicted with federal legislation on the same subject matter - specifically, the Smith Act which made it illegal to advocate for overthrowing the government. This ruling reinforced supremacy of federal law over state law when both levels of government legislate on identical issues; a principle known as preemption doctrine in American jurisprudence.

In the dissenting opinion for Pennsylvania v. Nelson, Justice Frankfurter argued that federal law did not necessarily preempt state sedition laws. He believed that states should retain the right to prosecute individuals for seditious activities if they so chose, as long as their actions were in line with constitutional requirements and did not interfere with federal objectives or operations. In his view, there was no evidence of Congress intending to exclude states from acting against sedition when it enacted the Smith Act (a federal statute outlawing advocacy of violent overthrow of government). Furthermore, he contended that allowing states this power would provide an additional safeguard against threats to national security without undermining any significant interest on part of the Federal Government.