14 CFR §374a.7

1. (a)Every air carrier subject to the part shall retain for 2 years after a Federal election true copies of the following documents at its principal or general office in the United States:
   1. (1)All documents which evidence or reflect the furnishing of transportation to a candidate for political office or a person acting on his behalf;
   2. (2)All statements, invoices, bills, and receipts with respect to the furnishing of such transportation referred to in paragraph (a)(1) of this section.
2. (b)Every air carrier shall make the documents listed in this section available in the United States upon request by an authorized representative of the DOT and shall permit such representative to make such notes and copies thereof as he deems appropriate.