49 U.S.C. § 41903 — Duty to provide certain transportation of mail

(a) Air Carriers. Subject to subsection (b), an airline certified to carry mail by air between places in Alaska must (1) have the facilities and services necessary and adequate to provide that transportation; and (2) carry the mail between the certified places whenever the Postal Service requires it, following the Postal Service's regulations. (b) Maximum Mail Load. The Secretary of Transportation can set the maximum amount of mail a schedule, aircraft, or type of aircraft can carry between places in Alaska. If the Postal Service offers an airline more mail than that maximum allows under a designated or required schedule, the airline must -- as closely to the schedule as the Secretary decides is possible -- (1) provide enough facilities to carry the mail, to the extent the Secretary decides the airline can reasonably do so; and (2) actually carry that mail.