49 C.F.R. § 1546.203 – Acceptance and screening of checked baggage.

(a) Preventing or deterring the carriage of any explosive or incendiary. Each foreign air carrier must use the procedures, facilities, and equipment described in its security program to prevent or deter the carriage of any unauthorized explosive or incendiary onboard aircraft in checked baggage.
(b) Refusal to transport. Each foreign air carrier must refuse to transport any individual's checked baggage or property if the individual does not consent to a search or inspection of that checked baggage or property in accordance with the system prescribed by this part.
(c) Firearms in checked baggage. No foreign air carrier may knowingly permit any person to transport, nor may any person transport, while aboard an aircraft being operated in the United States by that carrier, in checked baggage, a firearm, unless:
1. (1) The person has notified the foreign air carrier before checking the baggage that the firearm is in the baggage; and
2. (2) The baggage is carried in an area inaccessible to passengers.