Whenever the Secretary has reason to believe that any live poultry dealer has violated or is violating any provision of section 197 of this title or section 228b–1 of this title, he shall cause a complaint in writing to be served upon the live poultry dealer, stating his charges in that respect, and requiring the live poultry dealer to attend and testify at a hearing at a time and place designated therein, at least 30 days after the service of such complaint; and at such time and place there shall be afforded the live poultry dealer a reasonable opportunity to be informed as to the evidence introduced against him (including the right of cross-examination), and to be heard in person or by counsel and through witnesses, under such regulations as the Secretary may prescribe. Any person for good cause shown may, on application, be allowed by the Secretary to intervene in such proceeding, and appear in person or by counsel. At any time prior to the close of the hearing, the Secretary may amend the complaint; but in case of any amendment adding new charges, the hearing shall, on the request of the live poultry dealer, be adjourned for a period not exceeding 15 days.