Mont. Code Ann. § 13-37-209

Accounts kept by the campaign treasurer of a candidate or political committee may be inspected under reasonable circumstances before, during, or after the election to which the accounts refer by the campaign treasurer of any opposing candidate or political committee in the same electoral district. The right of inspection may be enforced by appropriate writ issued by any court of competent jurisdiction. The campaign treasurers of political committees supporting a candidate may be joined with the campaign treasurer of the candidate as respondents in such a proceeding.