Mich. Comp. Laws § 324.50166: Exemption from taxation.

Sec. 50166.

The state covenants with the purchasers and all subsequent holders and transferees of bonds issued under this part, in consideration of the acceptance of and payment for the bonds, that the bonds issued under this part and the income from those bonds and all its fees, charges, gifts, grants, revenues, receipts, and other money received or to be received, pledged to pay or secure the payment of the bonds at all times are exempt from state or local income taxation provided by the laws of the state, except for estate, inheritance, and gift taxes and taxes on transfers.