Mich. Comp. Laws § 123.812

Sec. 2. The agreements, subject to the approval of the governing bodies of the counties, cities, villages, or townships, shall provide for the nature of the emergency, who shall declare the emergency, under what circumstances police assistance may be asked for, and by which county, city, village, or township officials; and shall provide for the payment of the services and what powers, duties, and responsibilities, and under whose authority, policemen called to duty under the terms of the mutual aid assistance agreement shall serve.