Recent Arizona Immigration Law
Article 1, Section 8, Clause 4 states the Federal Government shall have the power "To establish an uniform Rule of Naturalization"
Since the power to establish rules of naturalization is delegated to the Federal Gvernment by the U S Constitution, it is a power that is reserved for the Federal Government.
Arizona is not trying to usurp Federal authority, they are simply ordering their police forces to notify the Federal Government of violations and enforce existing law(which Obama refuses to do).
Opponents of the law have used the argument that portions of it can be abused to discriminate against minorities, even though it specifically bans discriminiation. Abuse of the law doesn't invalidate it's constitutionality - it's simply abuse of the law. Any law can be abused and manipulated.