The Commissioner may ascertain what wage is paid in any occupation in the State. In an investigation under this subtitle, the Commissioner shall try to negotiate with an employer to obtain the testimony or documentary evidence that is needed to determine whether a violation exists. If the Commissioner is unable to obtain evidence by negotiation, the Commissioner may issue a subpoena for the attendance of a witness to testify or the production of documentary evidence that relates to the subject matter of the complaint. Each application for a subpoena under this subsection shall: be under oath; and describe in detail: the nature, purpose, and scope of the investigation; each witness to be subpoenaed; and each record to be inspected. A subpoena may not be issued unless the application is approved by the Attorney General as to form and substance. If a person fails to comply with a subpoena issued under this subsection, on a complaint filed by the Commissioner, a circuit court may compel compliance with the subpoena.