Missouri constitution
Article III: legislative department
Section 20(b)

Upon the filing with the secretary of state of a petition stating the
purpose for which the session is to be called and signed by three-fourths of the members
of the senate and three-fourths of the members of the house of representatives,
the president pro tem of the senate and the speaker of the house shall by joint proclamation
convene the general assembly in special session. The proclamation shall state
specifically each matter contained in the petition on which action is deemed necessary.
No appropriation bill shall be considered in a special session convened pursuant to
this section if in that year the general assembly has not passed the operating budget in
compliance with Section 25 of this article.
The general assembly shall automatically stand adjourned sine die at 6:00 p.m. on
the thirtieth calendar day after the date of its convening in special session under this
section unless it has adjourned sine die prior thereto.