Missouri constitution
Article III: legislative department
Section 52(b)

The veto power of the
governor shall not extend to measures referred to the people. All elections on measures
referred to the people shall be had at the general state elections, except when the general
assembly shall order a special election. Any measure referred to the people shall
take effect when approved by a majority of the votes cast thereon, and not otherwise.
This section shall not be construed to deprive any member of the general assembly of
the right to introduce any measure.