Mont. Code Ann. § 26-2-507

A witness is not obliged to attend court or appear before a referee, officer authorized to take depositions, or commissioner, when subpoenaed, unless the witness's mileage and fees for 1 day's attendance are tendered or paid to the witness on demand or unless the fees for attendance for each succeeding day are tendered or paid to the witness on demand. The fees of witnesses paid may be taxed as costs against the losing party.