Vessels entering or leaving a zone shall be subject to the operation of all the laws of the United States, except as otherwise provided in this chapter, and vessels leaving a zone and arriving in customs territory of the United States shall be subject to such regulations to protect the revenue as may be prescribed by the Secretary of the Treasury. Nothing in this chapter shall be construed in any manner so as to permit vessels under foreign flags to carry goods or merchandise shipped from one foreign trade zone to another zone or port in the protected coastwise trade of the United States.