Mont. Code § 69-14-1003
A conductor, engineer, or other person in charge of the operation of cars, trains, or locomotives upon any railroad is, while engaged or employed, a public executive officer of the class of peace officers and of the grade of constable in each county in which the train, cars, or locomotives are located and has the same authority as other peace officers to, with or without a warrant, arrest and prosecute persons trespassing or illegally obtaining passage on the railroad. The railroad personnel mentioned in this section are not entitled to receive fees for any arrest or prosecution that may be made or prosecuted under this section. None of the railroad personnel mentioned in this section are authorized to hold the office or exercise its functions unless at the time they are citizens of the United States and have been citizens of this state for at least 1 year preceding their exercising the functions of the office.
§ 69-14-1003, MCA