15 CFR § 904.242 - Interrogatories.
(a) Service and use. If ordered by the Judge, any party may serve upon any other party written interrogatories in conformance with § 904.3.
(b) Answers and objections. Answers and objections must be made in writing under oath, and reasons for the objections must be stated. Answers must be signed by the person making them and objections must be signed by the party or attorney making them. Unless otherwise ordered, answers and objections must be served on all parties within 20 days after service of the interrogatories in conformance with § 904.3.
(c) Option to produce records. Where the answer to an interrogatory may be ascertained from the records of the party upon whom the interrogatory is served, it is sufficient to specify such records and afford the party serving the interrogatories an opportunity to examine them.
(d) Use of interrogatories at hearing. Answers may be used at hearing in the same manner as depositions under § 904.241(d).