Nichols v. Levy was a United States Supreme Court case in which the court held that an individual could not be convicted of violating a state law if they had acted in good faith and under the authority of federal law. The case arose when Benjamin Nichols, who was employed by the U.S. Treasury Department to collect revenue from vessels entering San Francisco Bay, arrested two individuals for failing to pay customs duties on goods imported into California without first obtaining permission from local authorities as required by state law. The defendants argued that since their actions were authorized by federal statute, they should not have been subject to prosecution under California's laws; however, lower courts disagreed and found them guilty of violating state statutes. In its ruling reversing those convictions, the Supreme Court held that where there is conflict between federal and state legislation concerning matters within Congress' constitutional power over interstate commerce or foreign affairs—as it did here—the former must take precedence over any conflicting provisions enacted at the State level regardless of whether those involved acted with knowledge or intent regarding such conflicts

In Nichols v. Levy, the Supreme Court was tasked with determining whether a state court had jurisdiction to issue an injunction against a federal officer in order to prevent him from executing his duties under federal law. The majority opinion held that the state court did not have such authority and could not enjoin the officer from performing his official duties. However, Justice Field dissented on this point and argued that while it is true that states cannot interfere with or impede upon matters of exclusive federal concern, they are still allowed to exercise their own powers within their respective jurisdictions as long as those actions do not conflict with any laws enacted by Congress. He further argued that since there were no applicable congressional statutes at issue in this case, then it was perfectly reasonable for the state court to grant an injunction against the defendant in order to protect its citizens' rights under its own laws.