Officers empowered to expend, or direct the expenditure of, public money of the state shall not make any contract for any purpose which contemplates an expenditure of such money in excess of that authorized by law. However, the state or an agency of the state may enter into a contract of not exceeding ten years in duration for the purchase of coal to be used in facilities under the jurisdiction of the state or the state agency. The execution of the contract shall be contingent upon appropriations by the general assembly in sufficient amounts to meet the terms of the contract.
Iowa Code § 72.1