Neither the uniformity of duties clause of the Constitution, Art. I, § 8, cl. 1, nor the port preference clause, Art. I, § 9, cl. 6, require uniformity of import quotas between the mainland and Puerto Rico.
The President has authority under § 232(b) of the Trade Expansion Act of 1962 to impose separate quantitative restrictions on oil imports into the U.S. mainland and Puerto Rico, respectively.
Any system of separate quotas imposed under the Trade Expansion Act must be justified by national security concerns.
By implication, § 232(b) authorizes the President to impose quotas on shipments of oil from Puerto Rico to the U.S. mainland in order to make the separate import quotas effective.