Iowa Code § 819.2

If a person, in any state whose law makes provision for commanding persons within that state to attend and testify in criminal actions pending or grand jury investigations commenced in this state, is a material witness in a district court action pending or a grand jury investigation commenced in this state, a judge of such court shall, in order to obtain the presence of such witness, issue a certificate under the seal of the court stating these facts and specifying the number of days the witness will be required.