14 C.F.R. § 91.709
No person may operate a civil aircraft from the United States to Cuba unless—
(b) In the case of departure from any of the 48 contiguous States or the District of Columbia, the pilot in command of the aircraft has filed—
(2) A written statement, within 1 hour before departure, with the Office of Immigration and Naturalization Service at the airport of departure, containing—
(iv) A description of the cargo, if any.
This section does not apply to the operation of aircraft by a scheduled air carrier over routes authorized in operations specifications issued by the Administrator.
(Approved by the Office of Management and Budget under control number 2120-0005)