Mich. Const. art. IX, § 31

Units of Local Government are hereby prohibited from levying any tax not authorized by law or charter when this section is ratified or from increasing the rate of an existing tax above that rate authorized by law or charter when this section is ratified, without the approval of a majority of the qualified electors of that unit of Local Government voting thereon. If the definition of the base of an existing tax is broadened, the maximum authorized rate of taxation on the new base in each unit of Local Government shall be reduced to yield the same estimated gross revenue as on the prior base. If the assessed valuation of property as finally equalized, excluding the value of new construction and improvements, increases by a larger percentage than the increase in the General Price Level from the previous year, the maximum authorized rate applied thereto in each unit of Local Government shall be reduced to yield the same gross revenue from existing property, adjusted for changes in the General Price Level, as could have been collected at the existing authorized rate on the prior assessed value.

The limitations of this section shall not apply to taxes imposed for the payment of principal and interest on bonds or other evidence of indebtedness or for the payment of assessments on contract obligations in anticipation of which bonds are issued which were authorized prior to the effective date of this amendment.