All controlled carriers shall be subject to provisions of this part and section 9 of the Shipping Act of 1984 (46 U.S.C. 40701-40706) except those which meet the following exceptions:

(a) When the vessels of the controlling state are entitled by a treaty of the United States to receive national or most-favored-nation treatment; or

(b) When the controlled carrier operates in a trade served exclusively by controlled carriers.