29 CFR 452.43: Representative categories.

In the case of a position which is representative of a unit defined on a geographic, craft, shift, or similar basis, a labor organization may by its constitution or bylaws limit eligibility for candidacy and for holding office to members of the represented unit. For example, a national or international labor organization may establish regional vice-presidencies and require that each vice-president be a member of his respective region. This kind of limitation would not be considered reasonable, however, if applied to general officers such as the president, vice-president, recording secretary, financial secretary, and treasurer. If eligibility of delegates to a convention which will elect general officers is limited to special categories of members, all such categories within the organization must be represented.