(a) Service and contents. In the interest of expedition and limited to information which appears reasonably calculated to lead to the discovery of admissible evidence, any party may propound to any other party in a proceeding written, sequentially numbered interrogatories, by witness, requesting non-privileged information relevant to the subject matter and reasonably calculated to lead to the discovery of admissible evidence in such proceeding, to be answered by the party served, who shall furnish such information as is available to the requesting party. A party through interrogatories may require any other party to identify each person whom the other party expects to call as a witness at the hearing and to state the subject matter on which the witness is expected to testify. The party propounding the interrogatories shall file them with the Commission and serve them on the answering party. Follow-up interrogatories to clarify or elaborate on the answer to an earlier discovery request may be filed after the initial discovery period ends. They must be filed within seven days of receipt of the answer to the previous interrogatory unless extraordinary circumstances are shown.

(b) Answers. Answers to discovery requests shall be prepared so that they can be incorporated as written cross-examination. Each answer shall begin on a separate page, identify the individual responding and the relevant testimony number, if any, the party who asked the question, and the number and text of the question. Each interrogatory shall be answered separately and fully in writing, unless it is objected to, in which event the reasons for objection shall be stated in the manner prescribed by paragraph (c) of this section. The party responding to the interrogatories shall file the answers with the Commission and serve them on the requesting party within 14 days of the filing of the interrogatories or within such other period as may be fixed by the Commission or presiding officer, but before the conclusion of the hearing.

(c) Objections. In the interest of expedition, the grounds for every objection shall be clearly and fully stated. If an objection is made to part of an interrogatory, the part shall be specified. A party claiming privilege shall identify the specific evidentiary privilege asserted and state the reasons for its applicability. A party claiming undue burden shall state with particularity the effort that would be required to answer the interrogatory, providing estimates of cost and work hours required, to the extent possible. An interrogatory otherwise proper is not necessarily objectionable because an answer would involve an opinion or contention that relates to fact or the application of law to fact, but the Commission or presiding officer may order that such an interrogatory need not be answered until a prehearing conference or other later time. Objections shall be filed with the Commission and served on the requesting party within ten days of the filing of the interrogatories. Any ground not stated in a timely objection is waived unless excused by the Commission or presiding officer for good cause shown.

(d) Motions to compel responses to discovery. Motions to compel a more responsive answer, or an answer to an interrogatory to which an objection was interposed, should be filed within 14 days of the answer or objection to the discovery request. The text of the discovery request, and any answer provided, should be provided as an attachment to the motion to compel. Parties who have objected to interrogatories which are the subject of a motion to compel shall have seven days to answer. Answers will be considered supplements to the arguments presented in the initial objection.

(e) Compelled answers. The Commission, or the presiding officer, upon motion of any party to the proceeding, may compel a more responsive answer, or an answer to an interrogatory to which an objection has been raised if the objection is overruled, or may compel an additional answer if the initial answer is found to be inadequate. Such compelled answers shall be filed with the Commission and served on the compelling party within seven days of the date of the order compelling an answer or within such other period as may be fixed by the Commission or presiding officer, but before the conclusion of the hearing.

(f) Supplemental answers. The individual or party who has answered interrogatories is under the duty to seasonably amend a prior answer if the individual or party obtains information upon the basis of which the individual or party knows that the answer was incorrect when made or is no longer true. Parties shall serve supplemental answers to update or to correct responses whenever necessary, up until the date the answer could have been accepted into evidence as written cross-examination. Parties filing supplemental answers shall indicate whether the answer merely supplements the previous answer to make it current or whether it is a complete replacement for the previous answer.

(g) Orders. The Commission or the presiding officer may order that any party or person shall answer on such terms and conditions as are just and may for good cause make any protective order, including an order limiting or conditioning interrogatories, as justice requires to protect a party or person from undue annoyance, embarrassment, oppression, or expense.