Mont. Code § 82-15-205
If a person presents to the county attorney of any county in which the discriminatory acts of a person, firm, company, association, or corporation have been committed a sworn written statement of the price paid, the date, and the parties selling and buying and reasonably reliable information of the price demanded or collected by the person, firm, company, association, or corporation for a corresponding or similar article of standard petroleum product sold or offered for sale in another part of the state of Montana or in the nearest adjoining state by the person, firm, company, association, or corporation, the county attorney shall promptly investigate and either commence and prosecute an action or furnish the informant with a written statement of reasons for not commencing and prosecuting an action under this part.
§ 82-15-205, MCA