Iowa Code § 29B.64: Rehearings.

1. If the convening authority disapproves the findings and sentence of a court-martial the convening authority may, except where there is lack of sufficient evidence in the record to support the findings, order a rehearing. In such case the convening authority shall state the reasons for disapproval. If the convening authority disapproves the findings and sentence and does not order a rehearing, the convening authority shall dismiss the charges.

2. Each rehearing shall take place before a court-martial composed of members not members of the court-martial which first heard the case. Upon a rehearing the accused may not be tried for any offense of which the accused was found not guilty by the first court-martial, and no sentence in excess of or more severe than the original sentence may be imposed, unless the sentence is based upon a finding of guilty of an offense not considered upon the merits in the original proceedings, or unless the sentence prescribed for the offense is mandatory.