Del. Code tit. 3 § 8531
An association may transact or do business with or for patron stockholders or patrons not stockholders, and may issue and sell its preferred stock to patrons or nonpatrons of the associations, but common stock of the association shall be sold to patrons only. The certificate of common stock shall contain a provision that the association shall have an option to redeem the stock at par value plus declared and unpaid dividends when the owner thereof has for a period of 12 months done no business with the association, and shall contain a further provision that no sale or transfer of stock shall be valid without the written consent of the association, and, if the association withholds its consent to such sale or transfer, then the association shall redeem such stock at par value plus declared and unpaid dividends.
3 Del. C. § 8531