Iowa Code § 356.29: Wages or salary collected by sheriff.

If a prisoner is employed for wages or salary the sheriff may collect the same or require the prisoner to turn over the wages or salary in full when received, and the sheriff shall deposit the same in a trust checking account and shall keep a ledger showing the status of the account of each prisoner. Such wages or salary are not subject to garnishment during the prisoner’s term and shall be disbursed only as provided in sections 356.26 through 356.35.