K.S.A. 50-116: Pleading in bar or abatement of civil action that plaintiff is member or agent of unlawful combination.

When an action at law or suit in equity shall be commenced in any court of this state, it shall be lawful in the defense thereof to plead in bar or in abatement that the plaintiff or any other person interested in the prosecution of the case is a member or agent of an unlawful combination as described in K.S.A. 50-112 and 50-113, or that the cause of action grows out of such combination, or out of some business or transaction thereof.