Iowa Code § 80.21: Fees and rewards.

No fees or rewards shall be retained personally by members of the department in addition to their salaries, and any such fees or rewards earned by any members of said department shall be credited to the fund as herein provided to pay the expenses of this department. All salaries herein provided for and all expenses incurred under the provisions of this chapter shall be allowed and audited in the same manner as in other state offices, and shall be payable out of moneys hereafter appropriated.