41 C.F.R. § 304-5.5

Agencies may authorize an employee to use other than coach class accommodations on common carriers as long as—

(a) The non-Federal source makes full payment for such transportation services in advance of travel;

(b) The transportation accommodations furnished are comparable in value to those offered to, or purchased by other similarly situated meeting attendees; and

(c) Travel meets at least one of the conditions in § 301-10.100 of this subtitle.