(a) Each person or carrier engaged in the transportation of mail shall carry on any vessel, train, motor vehicle, or aircraft he operates, upon exhibiting their credentials and without extra charge therefor, persons on duty in charge of the mails or when traveling to and from such duty. (b) (1) In this subsection, “ air carrier ” and “aircraft” have the same meanings given those terms in section 40102(a) of title 49 . (2) An air carrier engaged in transporting mail shall carry without charge on any plane it operates those agents and officers of the Postal Service traveling on official business related to transporting mail by aircraft, as prescribed by regulations of the Secretary of Transportation, on exhibiting credentials. ( Pub. L. 91–375 , Aug. 12, 1970 , 84 Stat. 768 ; Pub. L. 103–272, § 4(g)(1) , July 5, 1994 , 108 Stat. 1364 .) Editorial Notes Amendments 1994— Pub. L. 103–272 designated existing provisions as subsec. (a) and added subsec. (b). 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