29 CFR § 452.107 - Observers.
(a) Under the provisions of section 401(c), each candidate must be permitted to have an observer (1) at the polls and (2) at the counting of the ballots. This right encompasses every phase and level of the counting and tallying process, including the counting and tallying of the ballots and the totaling, recording, and reporting of tally sheets. If there is more than one polling place, the candidate may have an observer at each location. If ballots are being counted at more than one location or at more than one table at a single location, a candidate is entitled to as many observers as necessary to observe the actual counting of ballots. The observer may note the names of those voting so that the candidates may be able to ascertain whether unauthorized persons voted in the election. The observers should be placed so that they do not compromise, or give the appearance of compromising, the secrecy of the ballot. The observer is not required to be a member of the labor organization unless the union's constitution and bylaws require him to be a member. There is no prohibition on the use of alternate observers, when necessary, or on a candidate serving as his own observer. Observers do not have the right to count the ballots.
(b) The right to have an observer at the polls and at the counting of the ballots extends to all candidates for office in an election subject to title IV, i.e., this includes elections in intermediate bodies as well as elections in locals and national and international labor organizations.
(c) In any secret ballot election which is conducted by mail, regardless of whether the ballots are returned by members to the labor organization office, to a mail box, or to an independent agency such as a firm of certified public accountants, candidates must be permitted to have an observer present at the preparation and mailing of the ballots, their receipt by the counting agency and at the opening and counting of the ballots.
(d) Paying election observers is the responsibility of the candidate they represent unless the union has a rule providing for the payment of observers. If the union does have such a rule, it must be uniformly applied to all candidates.
https://www.law.cornell.edu/cfr/text/29/452.107