Mich. Comp. Laws § Article IX § 15: Long term borrowing by state.

Sec. 15.

The state may borrow money for specific purposes in amounts as may be provided by acts of the legislature adopted by a vote of two-thirds of the members elected to and serving in each house, and approved by a majority of the electors voting thereon at any general election. The question submitted to the electors shall state the amount to be borrowed, the specific purpose to which the funds shall be devoted, and the method of repayment.