Sometime people think that everything the Federal Government does is completely ok. But the reality is that the U.S. Constitution did not grant unlimited power to the federal government.
I fact, the united states of America are 50 sovereign states that granted some of their sovereign powers to the federal government and kept all the powers that were not specifically given up. (See the 10th Amendment to the Constitution.)
The following article is a good example of how States are acting to protect the sovereignty they did not give up.