What happens when the Supreme Court declares a government action (a rule or law) to be unconstitutional?

When the proper court determines that a legislative act (a law) conflicts with the constitution, it finds that law unconstitutional and declares it void in whole or in part. This is called judicial review. ... In these cases, only governments can violate the nation's constitution, but there are exceptions.

Explanation:

When the Supreme Court rules on a constitutional issue, that judgment is virtually final; its decisions can be altered only by the rarely used procedure of constitutional amendment or by a new ruling of the Court. However, when the Court interprets a statute, new legislative action can be taken. The judicial branch interprets laws and determines if a law is unconstitutional. The judicial branch includes the U.S. Supreme Court and lower federal courts. There are nine justices on the Supreme Court. Therefore, the Supreme Court has the final say in matters involving federal law, including constitutional interpretation, and can overrule decisions by state courts. ... The Court found that this would be inconsistent with the Supremacy Clause, which makes federal law superior to state law. The Court decided against Marbury 6-0. Historical significance: Chief Justice John Marshall wrote, "An act of the legislature repugnant to the constitution is void." It was the first time the Supreme Court declared unconstitutional a law that had been passed by Congress. The Supreme Court and other federal courts (judicial branch) can declare laws or presidential actions unconstitutional, in a process known as judicial review. By passing amendments to the Constitution, Congress can effectively check the decisions of the Supreme Court.

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