Iowa constitution
Article III
Section 32

Members of the general assembly shall, before they enter upon the duties of their respective offices, take and subscribe the following oath or affirmation: "I do solemnly swear, or affirm, (as the case may be,) that I will support the Constitution of the United States, and the Constitution of the State of Iowa, and that I will faithfully discharge the duties of senator, (or representative, as the case may be,) according to the best of my ability." And members of the general assembly are hereby empowered to administer to each other the said oath or affirmation.