49 C.F.R. § 209.205 – Reply.

(a) Within thirty (30) days of service of a notice of investigation, the respondent may file a reply with the FRA. The Chief Counsel may extend the time for filing for good cause shown.
(b) The reply must be in writing, signed by the person filing it, and state with respect to each factual allegation whether it is admitted or denied. Even though formally denied, a factual allegation set forth in a notice of investigation is considered to be admitted for purposes of the proceeding unless:
1. (1) Opposed by the affidavit of an individual having personal knowledge of the subject matter;
2. (2) Challenged as defective on its face together with a supporting explanation as to why it is believed to be defective; or
3. (3) Otherwise actively put at issue through the submission of relevant evidence.
(c) The reply must set forth any affirmative defenses and include a statement of the form and nature of proof by which those defenses are to be established.
(d) If it is necessary to respond to an amendment to the notice of investigation, the respondent may amend the reply concerning the substance of matters contained in the amendment to the notice at any time before the issuance of an order under § 209.211.
(e) If the respondent elects not to contest one or more factual allegations, he or she should so state in the reply. An election not to contest a factual allegation is an admission of that allegation solely for the purpose of issuing a compliance order. That election constitutes a waiver of hearing as to that allegation but does not, by itself, constitute a waiver of the right to be heard on other issues. In connection with a statement of election not to contest a factual allegation, the respondent may propose an appropriate order for issuance by the Administrator or propose the negotiation of a consent order.
(f) Failure of the respondent to file a reply within the period provided constitutes a waiver of his or her right to appear and contest the allegation and authorizes the Administrator, without further notice to the respondent, to find the facts to be as alleged in the notice of proposed violation and to issue an appropriate order directing compliance.