14 CFR § 250.3 - Boarding priority rules.
(a) Every carrier shall establish priority rules and criteria for determining which passengers holding confirmed reserved space shall be denied boarding on an oversold flight in the event that an insufficient number of volunteers come forward. Such rules and criteria shall reflect the obligations of the carrier set forth in §§ 250.2a and 250.2b to minimize involuntary denied boarding and to request volunteers, and shall be written in such manner as to be understandable and meaningful to the average passenger. Such rules and criteria shall not make, give, or cause any undue or unreasonable preference or advantage to any particular person or subject any particular person to any unjust or unreasonable prejudice or disadvantage in any respect whatsoever.
(b) Boarding priority factors may include, but are not limited to, the following:
(1) A passenger's time of check-in;
(2) Whether a passenger has a seat assignment before reaching the departure gate for carriers that assign seats;
(3) The fare paid by a passenger;
(4) A passenger's frequent-flyer status; and
(5) A passenger's disability or status as an unaccompanied minor.
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