Neb. Rev. Stat. § 16-215: Neb. Rev. Stat. § 16-215

A city of the first class may make provision for a sinking fund to pay accruing interest and to pay at maturity the principal of the bonded indebtedness of the city, levy and collect taxes on all the taxable property in the city, in addition to other taxes, for the purpose of paying the same, and provide that the tax shall be paid in cash.