Iowa Code § 29A.22
The moral character, capacity and general fitness for the service of any national guard officer may be determined at any time by an efficiency board as provided by federal law and regulations. Commissions or warrants of officers of the national guard may be vacated upon resignation, absence without leave for three months, upon the recommendation of an efficiency board, or pursuant to sentence of a court-martial. Any officer permanently removing from the state shall resign the officer's commission or warrant upon request of the adjutant general or make application to be placed upon the inactive list, and upon failure to do so, the officer's commission or warrant shall be revoked by the governor. Officers rendered surplus by the disbandment of their organization shall be disposed of as provided by law and regulations. Subject to the approval of their superior commanders and the adjutant general, officers may, upon their own application, be placed on the inactive list, as such list may be authorized by law and regulations.
Iowa Code § 29A.22