Minn. Stat. § 243.61

No contracts for leasing the labor of prisoners confined in any such institution, at a certain rate per diem, giving the contractor full control of the labor of the prisoners, shall be made; but such prisoners shall be employed, under rules established by the commissioner of corrections, in such industries as shall, from time to time, be fixed upon by the officers in charge and the commissioner, or in the manufacture of articles by the piece, under the so-called "piece price system," by contracts with persons furnishing the materials. The chief officer, under the direction of the commissioner, shall purchase such tools, implements, and machinery as the officer shall deem necessary for the work.