Iowa Code § 519.2

All corporations, organized for the purpose of transacting such insurance business under the provisions of this chapter, shall incorporate under the provisions of chapter 491, and be known as mutual corporations; and are hereby empowered to collect such assessments, or premium payments, provided for in their articles of incorporation or bylaws, as are required to pay losses and expenses incurred in the conduct of their business and to cede reinsurance. Such mutual insurance corporations may issue certificates of membership, or policies; and may provide that all assessments, or premium payments, payable thereunder, be made in cash, or on the installment, or assessment plan.