Mich. Comp. Laws § 205.54h

Sec. 4h. Sales to the United States, its unincorporated agencies and instrumentalities, any incorporated agency or instrumentality of the United States wholly owned by the United States or by a corporation wholly owned by the United States, the American Red Cross and its chapters and branches, and this state or its departments and institutions or any of its political subdivisions are exempt from the tax under this act.