In making investigations herein authorized the Department may hold public hearings. Any hearing may be conducted by the Department or by a committee appointed by it, consisting of one or more members of the Department, or by an employee or agent specially authorized by the Department to conduct it. The Department and any member, employee or agent thereof so designated shall have power to administer oaths, take affidavits, subpoena and require the attendance and testimony of witnesses and the production of books and papers pertaining to such investigation.