Wis. Stat. § 168.10: Access to records.

Every agent or employee of any railroad company or other transportation company and every person transporting gasoline, gasoline-alcohol fuel blends, kerosene, other refined oils, fuel oils and petroleum distillates, having the custody of books or records showing the shipment or receipt of gasoline, gasoline-alcohol fuel blends, kerosene, or other refined oils, fuel oils and petroleum distillates shall give and permit the department and the inspectors; and, in regard to the fee under s. 168.12 (1), shall give and permit the department of revenue; free access to such books and records for the purpose of determining the amount of petroleum products shipped and received. All clerks, bookkeepers, express agents, railroad agents or officials, employees, or common carriers, or other persons shall provide the department and the inspectors; and, in regard to the fee under s. 168.12 (1), shall provide the department of revenue; all information in their possession when so requested in tracing, finding, sampling and inspecting such shipments.