Mont. Code Ann. § 15-39-105
Penalties and interest for violation
15-39-105 . Penalties and interest for violation. (1) (a) A person who fails to file a statement as required by 15-39-102 must be assessed a penalty as provided in 15-1-216 . The department may waive the penalty as provided in 15-1-206 .
(b) A person who fails to file the statement required by 15-39-102 and to pay the tax on or before the due date must be assessed a penalty and interest as provided in 15-1-216 . The department may waive any penalty pursuant to 15-1-206 .
(2) A person who purposely fails to pay the tax when due must be assessed an additional penalty as provided in 15-1-216 .