19 CFR 122.165: Air cabotage.

(a) The air cabotage law (49 U.S.C. 41703) prohibits the transportation of persons, property, or mail for compensation or hire between points of the U.S. in a foreign civil aircraft. The term “foreign civil aircraft” includes all aircraft that are not of U.S. registration except those foreign-registered aircraft leased or chartered to a U.S. air carrier and operated under the authority of regulations issued by the Department of Transportation, as provided for in 14 CFR 121.153, and those aircraft used exclusively in the service of any government.

(b) Customs officers detecting possible violations shall report the matter to Headquarters, Attention: Entry Procedures and Carriers Branch. Liability should not be assessed under 49 U.S.C. Chapter 463 pending instructions from Headquarters since certain limited domestic transportation by foreign civil aircraft is permitted under regulations issued by the Department of Transportation.