A state law provided that only citizens of the United States may be hired by any governmental unit within the state. A citizen of the Philippines, who had been a legal resident of the state for five years, was awarded a medical degree from the state university and was licensed by the state to practice medicine. The doctor applied for a job opening in the state government, but despite the fact that she was fully qualified, she was rejected solely because of the statute. If she files suit in federal court to enjoin enforcement of the statute, what is her best constitutional argument