Mo. Const. art. VI, § 26(c)

Any county or city, by vote of the qualified electors thereof voting thereon, may incur an additional indebtedness for county or city purposes not to exceed five percent of the taxable tangible property shown as provided in section 26(b). For elections referred to in this section the vote required shall be four-sevenths at the general municipal election day, primary or general elections and two-thirds at all other elections. [Effective - 01 Sep 1988 , see footnote]