29 C.F.R. § 6.31
At any time prior to the closing of the hearing record, the complaint (notification letter) or answer (response) may be amended with the permission of the Administrative Law Judge and upon such terms as he/she may approve. For proceedings pursuant to § 5.11 of part 5 of this title, such an amendment may include a statement that debarment action is warranted under § 5.12(a)(1) of part 5 of this title or under section 3(a) of the Davis-Bacon Act. Such amendments shall be allowed when justice and the presentation of the merits are served thereby, provided there is no prejudice to the objecting party's presentation on the merits. When issues not raised by the pleadings are reasonably within the scope of the original complaint and are tried by express or implied consent of the parties, they shall be treated in all respects as if they had been raised in the pleadings, and such amendments may be made as necessary to make them conform to the evidence. The presiding Administrative Law Judge may, upon reasonable notice and upon such terms as are just, permit supplemental pleadings setting forth transactions, occurrences or events which have happened since the date of the pleadings and which are relevant to any of the issues involved. A continuance in the hearing may be granted or the record left open to enable the new allegations to be addressed.
29 C.F.R. §6.31