When a state refuses to follow a federal law, it is called

Nullification is the name given to the action whereby a state refuses to follow a federal law. Under this the state decides that a federal law is unconstitutional and thereby does not follow the law. 

The correct answer is nullification

This was a process that was very popular in politics in earlier times, such as the 19th century, but it is not talked about as much nowadays. The states believed that if they perceive a federal law to be tyrannical that they can apply nullification which in laymen terms means that they just wouldn't adopt it or adhere by it.