30 V.S.A. § 18

So far as is necessary for the performance of its duties, the Public Utility Commission or the Commissioner of Public Service, the Directors for Public Advocacy and Regulated Utility Planning, and any other employee of the Department authorized by the Commissioner shall have power to examine the books, accounts, and papers of any company, receiver, trustee, or lessee owning or operating any line, plant, or property, subject to the Commission's or the Department's jurisdiction that in any way relate to or contain entries, data, or memoranda concerning any transaction substantially affecting the interests of the State of Vermont or consumers of utility services within the State, to subpoena witnesses, to administer oaths to them, and to examine them on all matters of which the Commission or Department has jurisdiction.