Mont. Code Ann. § 42-2-209

A person filing a registration form is presumed to be the father of the child for purposes of adoption unless the mother denies that the registrant is the father. The registration or any revocation that is filed is admissible in a paternity proceeding and creates a rebuttable presumption as to the paternity of the child. The registration creates a rebuttable presumption as to paternity of the child for purposes of an abuse or neglect proceeding under Title 41, chapter 3, or a child support enforcement action under Title 40, chapter 5.