Contracts for the transportation of mail by vessel between the United States and a foreign port shall be made subject to cancellation by the Postal Service or the Congress . ( Pub. L. 91–375 , Aug. 12, 1970 , 84 Stat. 773 .) Statutory Notes and Related Subsidiaries Effective Date Section effective July 1, 1971 , pursuant to Resolution No. 71–9 of the Board of Governors. See section 15(a) of Pub. L. 91–375 , set out as a note preceding section 101 of this title . CFR Title Parts 39 601