What is it called when a state rejects a federal law?

Answer 1

It's called the Doctrine of Nullification. The theory states that a state has the right to nullify or declare void any Federal law that it deems to be unconstitutional. Although there is no clause in the US Constitution stating who has the right to declare a Federal law to be unconstitutional, precedent had given that power to the US Supreme Court alone. However since there is no direct Constitutional clause (only indirectly through the Supremacy Clause), the right of the Supreme Court to be the sole arbiter of the constitutionality of a law was highly controversial. Nullification was a hot political issue on the first half of the 19th century. The controversy surrounding nullification indirectly led to the American Civil War. After the Civil War was over, nullification ceased to be a major political issue though it has arisen several times since then and has never entirely gone away.