Minn. Stat. § 175.24

On request of the Department of Labor and Industry, and within the time limited therein, every employer of labor, any officer of a labor organization, or any person from whom the Department of Labor and Industry shall find it necessary to gather information, shall make a certified report to the department, upon blanks furnished by it, of all matters covered by the request. The names of persons or concerns supplying such information shall not be disclosed. Every notice, order, or direction given by such department shall be in writing, signed by an officer or inspector of such department, or a person specially designated for the purpose, and be served by the signer. Papers so served and all records and documents of the department are hereby declared public documents and shall not be destroyed within two years after their return or receipt by such department.