The commissioner or an authorized representative may enter without unreasonable delay and inspect places of employment, during normal working hours, and investigate facts, conditions, practices or matters as the commissioner deems appropriate to enforce the laws within the commissioner’s jurisdiction and to carry out the purposes of this chapter and chapter 177, 181, 181A, or 184. If an employer refuses to permit entry into the employer’s place of employment, the commissioner may apply for an inspection order in the district court in the county in which the place of employment is located requiring the employer to permit entry of the commissioner or an authorized representative. The commissioner or an authorized representative may issue subpoenas, collect evidence, interview witnesses, take testimony, compel the attendance of witnesses, and shall have authority to administer oaths and take testimony under oath, but no person shall be compelled to attend as a witness unless paid the fees provided for witnesses in the district court. The commissioner may interview in private nonmanagement employees regarding the matter under investigation.