14 CFR § 212.5 - Operation of affinity (pro rata) charters.
(a) The aircraft must be chartered by an organization, no part of whose business is the formation of groups for transportation or solicitation or sale of transportation services, for the purpose of providing air transportation to its members and their immediate families.
(b) The charter must be organized by the organization itself, or by a person or company who acts not as a principal, but as an agent for the chartering organization or the certificated or foreign air carrier.
(c) No solicitation, sales, or participation may take place beyond the bona fide members of an eligible chartering organization, and their immediate families (spouse, children, and parents). All printed solicitation materials shall contain the following notice in boldface, 10-point or larger type -
Some of the Federal rules that protect against tour changes and loss of passengers' money in publicly sold charters do not apply to this charter flight.
(d) “Bona fide members” are members of an organization who: Have not joined the organization merely to travel on a charter flight; and who have been members of the chartering organization for a minimum of six months prior to the date of commencement of the affected flight; provided, that the “six month” rule does not apply to:
(1) Employees of a single commercial establishment, industrial plant, or government agency, or
(2) Students and employees of a single school.
(e) The charter price due the direct air carrier shall be prorated equally among all the charter passengers, except that children under 12 may be offered discounted or free transportation.
(f) The certificated or foreign air carrier shall make reasonable efforts to assure that passengers transported meet the eligibility requirements of this section. The certificated or foreign air carrier shall also obtain (no later than the date of departure), and maintain for two years, a certification by an authorized representative of the chartering organization that all passengers are eligible for transportation under this section.