25 C.F.R. § 81.35
When must the Secretarial Election Board send ballots to voters?
(a) Unless the amendment or adoption articles of the tribe's governing document require the use of polling sites in the election, the election must be conducted entirely by mailout ballots, and the Secretarial Election Board must send mailout ballots to registered voters promptly upon completion of the Registered Voters List.
(b) When the amendment or adoption articles of the tribe's governing document require the use of polling sites in the election, the Secretarial Election Board must send an absentee ballot to every registered voter who requests an absentee ballot, as long as the request is received before the Secretarial election date.
(c) All mailout or absentee ballot deliveries must be via U.S. Mail or by hand-delivery to the location identified in the Secretarial election notice before the date of the Secretarial election.