Nowhere does the constitution say that. The Supremacy Clause says only constitutional federal laws are above state laws but it doesn't directly say who decides the constitutionality. THINK
Thus....any law, not found to be "unconstitutional" is what? Enforceable in every state of the union? Or are you suggesting that there are no constitutional laws drafted by the only body authorized to draft law...the legislative branch? Your statement is OXYMORONIC to say the least.

If STATE LAW is the only law enforceable in a state....why Have a Federal Legislative Branch? Why have state representatives draft and ratify these federalist laws? Why send them to DC to draft useless laws?
The Constitution is clear, the federal legislative branch has the authority to, "To make all laws which shall be necessary and proper for the carrying into execution the forgoing powers, and all other powers vested by this constitution in the Government of the United States or any Department or officer thereof." -- Section 8
What...you don't think that "run-a-way" illegal immigration pertains to the GENERAL WELFARE or COMMON DEFENSE of the entire nation? Border security and immigration are both paramount to both the General Welfare and Common Defense of the entire nation. No one state can enforce the entire border security....nor can any one state by itself protect the entire nation from the crime of illegal immigration that places the entire nation in danger with the declared war on terror. There are many things that the General Welfare and Common Defense should not cover like a blanket...like farm trade and labor etc., but Securing the Border in a time of war certainly falls into the execution of the General Welfare and Common Defense Clause of Section 8.
Thus....immigration law is both constitutional and enforceable in all states of this REPUBLICAN UNION. Because its represented....ratified law...i.e., the standing rule of law. Even Amendment 10 details the fact that the states give the central government power by the authority of the PEOPLE/STATES..these laws are concessions expressly made to the federal government by the states.
Who decides the Constitutionality of a law? The law itself....if that drafted and ratified law does not conflict with the written contract known as the United States Constitution. Its Constitutional. The courts duty is to compare law against the actual words of the constitution. There is no authority for anyone to "interpret" the constitution....the constitution is to be enforced as written....or enforced as amended..with the only method of amending the constitution...Adding or taking away words....coming from THE PEOPLE by a 75% super majority ratification process.