Mont. Code Ann. § 15-70-418

If a distributor files a false or fraudulent return with intent to evade the tax imposed by this part, there is added to the amount of deficiency determined by the department of transportation a penalty equal to 25% of the deficiency, together with interest at the rate of 1% a month, prorated daily, on the deficiency from the date the tax was due to the date of payment, in addition to all other penalties prescribed by law.