39 U.S.C. § 5605
Contracts for transportation of mail by vessel
The Postal Service may contract for the transportation of mail by vessel without advertising for bids.
( Pub. L. 91–375 , Aug. 12, 1970 , 84 Stat. 773 ; Pub. L. 109–435, title X, § 1002(b)(3) , Dec. 20, 2006 , 120 Stat. 3255 .)