Iowa Const. art. VII, § 5

Except the debts herein before specified in this article, no debt shall be hereafter contracted by, or on behalf of this state, unless such debt shall be authorized by some law for some single work or object, to be distinctly specified therein; and such law shall impose and provide for the collection of a direct annual tax, sufficient to pay the interest on such debt, as it falls due, and also to pay and discharge the principal of such debt, within twenty years from the time of the contracting thereof; but no such law shall take effect until at a general election it shall have been submitted to the people, and have received a majority of all the votes cast for and against it at such election; and all money raised by authority of such law, shall be applied only to the specific object therein stated, or to the payment of the debt created thereby; and such law shall be published in at least one newspaper in each county, if one is published therein, throughout the state, for three months preceding the election at which it is submitted to the people.