Wis. Stat. § 196.25

(1) If a public utility receives from the commission any questionnaire, the public utility shall respond fully, specifically and correctly to each question. If a public utility is unable to answer any question, the public utility shall give a good and sufficient reason for its failure. Every answer by a public utility under this section shall be verified under oath by the president, secretary, superintendent or general manager of the public utility and returned to the commission at its office within the period fixed by the commission.

(2) If required by the commission, a public utility shall deliver to the commission the original or a copy of any map, profile, contract or engineer's report and any other document, book, account, paper or record with a complete inventory of all its property, in such form as the commission directs.

(3) If a telecommunications provider receives a questionnaire from the commission, the telecommunications provider shall respond specifically, correctly and fully to each question. If a telecommunications provider is unable to answer any question, the telecommunications provider shall give a good and sufficient reason for its failure. Answers shall be verified under oath by the president, secretary, superintendent or general manager of the telecommunications provider. A completed questionnaire shall be returned to the commission within the time period specified by the commission.