Mich. Comp. Laws § 124.469

Sec. 19. Any member of the public authority or a political subdivision otherwise granted taxing authority under state law may levy a tax on all of the taxable property within the limits of the political subdivision, and appropriate, grant, or contribute the proceeds of the tax to the public authority for public transportation purposes as authorized by this act or to provide sufficient money to fulfill its contractual obligation to the public authority under section 20, which tax shall be within charter, statutory, and constitutional limitations.