Mont. Code Ann. § 32-1-373

Any bank is hereby authorized and empowered to join or associate itself with the federal reserve bank, or any branch thereof, and nothing herein contained shall prevent or prohibit any bank from joining or associating itself with any such banks or branch thereof or from investing any part of its capital or surplus in the stock of such bank, in accordance with the terms and provisions of the act of congress creating such association. Any bank joining or associating itself with such bank shall be permitted to conform to and transact its business in accordance with the terms and provisions of the act of congress creating the same and the rules of such federal reserve bank.