Mo. Rev. Stat. § 386.450
At the request of the public counsel and upon good cause shown by him the commission shall require or on its own initiative the commission may require, by order served upon any corporation, person or public utility in the manner provided herein for the service of orders, the production within this state at such time and place as it may designate, of any books, accounts, papers or records kept by said corporation, person or public utility in any office or place within or without this state, or, at its option, verified copies in lieu thereof, so that an examination thereof may be made by the public counsel when the order is issued at his request or by the commission or under its direction.
§ 386.450, RSMo
RSMo 1939 § 5700, A.L. 1977 H.B. 42 & 157