18 U.S.C. § 1698

Whoever, having charge or control of any vessel passing between ports or places in the United States, and arriving at any such port or place where there is a post office, fails to deliver to the postmaster or at the post office, within three hours after his arrival, if in the daytime, and if at night, within two hours after the next sunrise, all letters and packages brought by him or within his power or control and not relating to the cargo, addressed to or destined for such port or place, shall be fined under this title.