(a) The Consumer Services Administration may investigate the prices at which all articles of food and general supplies are sold or purchased by importers, merchants, dealers, producers, manufacturers or consumers.
(b) For the purpose of subsection (a) of this section, the invoices of all such persons shall be opened to inspection by the Consumer Services Administration and, if necessary, it may issue subpoenas for the attendance of witnesses or for the production of invoices or other documents, and shall have the power to take testimony under oath.