(a) Unless otherwise limited by order of the Agency Decisionmaker or, in cases that have been called for a hearing, the administrative law judge, in accordance with these rules, the parties may obtain discovery regarding any matter, not privileged, which is relevant to the subject matter involved in the proceeding, including the existence, description, nature, custody, condition, and location of any books, documents, or other tangible things and the identity and location of persons having knowledge of any discoverable matter.

(b) It is not ground for objection that information sought will not be admissible at the hearing if the information sought appears reasonably calculated to lead to the discovery of admissible evidence.

(c) A party may obtain discovery of documents and tangible things otherwise discoverable under paragraph (a) of this section and prepared in anticipation of or for the hearing by or for another party's representative (including his or her attorney, consultant, surety, indemnitor, insurer, or agent) only upon a showing that the party seeking discovery has substantial need of the materials in the preparation of his or her case and that he or she is unable without undue hardship to obtain the substantial equivalent of the materials by other means. In ordering discovery of such materials when the required showing has been made, the Agency Decisionmaker or the administrative law judge shall protect against disclosure of the mental impressions, conclusions, opinions, or legal theories of an attorney or other representative of a party concerning the proceeding.