Neb. Rev. Stat. § 44-3106

No professional association mutual insurance company shall be issued a certificate of authority to do any business in this state until it has filed with the director acceptable evidence that it has and will maintain a minimum surplus aggregating at least five hundred thousand dollars in cash in the investments authorized under the Insurers Investment Act or a letter of credit issued by a Nebraska banking institution in accordance with loan restrictions prescribed by the laws of this state.