Mont. Code Ann. § 30-13-331

The secretary of state shall adopt rules establishing a classification of goods and services for convenience of administration of this part. The classification does not limit or extend the applicant's or registrant's rights. A single application for registration of a mark may include any or all goods upon which or services with which the mark is actually being used indicating the appropriate class or classes of goods or services. When a single application includes goods or services that fall within multiple classes, the secretary of state may require payment of a fee for each class. To the extent practical, the classification of goods and services must conform to the classification adopted by the United States patent and trademark office.