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

A referendum may be
ordered (except as to laws necessary for the immediate preservation of the public
peace, health or safety, and laws making appropriations for the current expenses of
the state government, for the maintenance of state institutions and for the support of
public schools) either by petitions signed by five percent of the legal voters in each
of two-thirds of the congressional districts in the state, or by the general assembly, as
other bills are enacted. Referendum petitions shall be filed with the secretary of state
not more than ninety days after the final adjournment of the session of the general
assembly which passed the bill on which the referendum is demanded.