29 C.F.R. § 452.86

A labor organization may condition the exercise of the right to vote upon the payment of dues, which is a basic obligation of membership. Such a rule must be applied uniformly. If a member has not paid his dues as required by the labor organization's constitution or bylaws he may not be allowed to vote. Thus, a rule which suspends a member's right to vote in an election of officers while the member is laid off and is not paying dues would not, in ordinary circumstances, be considered unreasonable, so long as it is applied in a nondiscriminatory manner. However, members must be afforded a reasonable opportunity to pay dues, including a grace period during which dues may be paid without any loss of rights. In the case where a member is laid off but desires to maintain his good standing and thus his membership rights by continuing to pay dues, it would be clearly unreasonable for the labor organization to refuse to accept his payment.