Mich. Comp. Laws § 484.3222

Sec. 22. This state covenants with the purchasers and all subsequent holders and transferees of notes and bonds issued by the authority, in consideration of the acceptance of and payment for the notes and bonds, that the notes and bonds of the authority, issued under this act and the income from the notes and bonds and all its fees, charges, grants, revenues, receipts, and other money received or to be received, pledged to pay or secure the payment of the notes or bonds shall at all times be free and exempt from all state, city, county, or other taxation provided by the laws of this state, except for estate and gift taxes and taxes on transfers.