Montana Constitution Art. III, § 5. Referendum

(1) The people may approve or reject by referendum any act of the legislature except an appropriation of money. A referendum shall be held either upon order by the legislature or upon petition signed by at least five percent of the qualified electors in each of at least one-third of the legislative representative districts. The total number of signers must be at least five percent of the qualified electors of the state. A referendum petition shall be filed with the secretary of state no later than six months after adjournment of the legislature which passed the act.

(2) An act referred to the people is in effect until suspended by petitions signed by at least 15 percent of the qualified electors in a majority of the legislative representative districts. If so suspended the act shall become operative only after it is approved at an election, the result of which has been determined and declared as provided by law.