SECTION 4A. Service upon board, commission or voluntary association

If a defendant in an action authorized by section four is a board or commission or voluntary association having a chairman or other presiding officer, secretary or clerk, by whatever official title he is called, service upon one of such persons shall be sufficient, otherwise service shall be made upon a majority of the members of a board or commission, or, as to a voluntary association on such of its members as will fairly insure the adequate representation of all.