731.3  Contracts to exclude unlawful.
  It shall be unlawful for any person, firm, association, corporation or labor organization to enter into any understanding, contract, or agreement, whether written or oral, to exclude from employment members of a labor union, organization or association, or persons who do not belong to, or who refuse to join, a labor union, organization or association, or because of resignation or withdrawal therefrom.
[C50, 54, 58, 62, 66, 71, 73, 75, 77, §736A.3; C79, 81, §731.3]