Iowa Code § 2.23: Witness — attendance compulsory.

Whenever a committee of either house, or a joint committee of both, is conducting an investigation requiring the personal attendance of witnesses, any person may be compelled to appear before such committee as a witness by serving an order upon the person, which service shall be made in the manner required in case of a subpoena in a civil action in the district court. Such order shall state the time and place a person is required to appear, be signed by the presiding officer of the body by which the committee was appointed, and attested by its acting secretary or clerk; or, in case of a joint committee, signed and attested by such officers of that body.