29 CFR §452.95

Where the union knows in advance that a substantial number or a particular segment of the members will not be able to exercise their right to vote in person, as, for example, when access to a polling place is impracticable for many members because of shipping assignments, absentee ballots or other means of voting must be made available. 45 In the event absentee ballots are necessary the organization must give its members reasonable notice of the availability of such ballots. 46