To protest human rights abuses in a foreign country, a state passes a law prohibiting companies doing business with that country or its citizens who travel to that country from bidding on state contracts. Congress enacted a similar law, though its statute does not sanction individuals for merely traveling to that country. If a reviewing judge strikes down the state statute it is likely because:

The state statute poses an obstacle to congressional aims in the area of foreign policy.

The state statute is expressly preempted by the congressional statute.

It is impossible to comply with both federal and state laws.

Congress has preempted the field of civil rights law