30 V.S.A. § 28

For the purpose of ascertaining the correctness of any return or for the purpose of making an estimate of the taxes due from any company, the Department of Public Service shall have power to examine or cause to be examined by any agent or representative designated by it for that purpose any books, papers, records, or memoranda of the company or of any person or corporation in the State bearing upon the matters required to be included in the return, and may require the attendance of any person having knowledge in the premises, at any place in the county where such person resides, and may take testimony and require proof material for its information, with power to administer an oath to such person.