18 C.F.R. § 385.908 – Discovery (Rule 908).

(a) By petitioner. In the answer under Rule 906(b)(2) (pleadings), the petitioner may request permission of the presiding officer to conduct discovery, where such discovery:
1. (1) Relates to new facts or issues raised in accordance with Rule 907(a) (new facts and issues); or
2. (2)
  1. (i) Was not permitted in the prior proceedings on the contested order due to erroneous adverse procedural rulings; and
  2. (ii) Is necessary for a full and true disclosure of the facts.
(b) By the Secretary. In the reply under Rule 906(a)(2) (pleadings), the Secretary may request permission of the presiding officer to conduct discovery where such discovery relates to new facts or issues raised in accordance with Rule 907(b) (new facts and issues).
(c) By interveners. In a motion to intervene under Rule 906(c)(8) (pleadings) an intervener may request permission of the presiding officer to conduct discovery where such discovery:
1. (1) Relates to new facts or issues raised in accordance with Rule 907(c) (new facts and issues); or
2. (2) If the intervener participated in the prior proceedings,
  1. (i) Such discovery was not permitted in prior proceedings on the contested order due to erroneous adverse procedural rulings; and
  2. (ii) Such discovery is necessary for a full and true disclosure of the facts.
(d) Determinations by the presiding officer. The presiding officer will determine whether to grant or deny, in whole or in part, the requests of the participants for discovery and will set a time limit within which discovery must be conducted.
(e) Interrogatories. In addition to discovery devices applicable to this subpart under other subparts of this part, participants may conduct discovery by means of written interrogatories under conditions determined by the presiding officer.