(a) Contents. The denial of registration or a notice of intent to cancel a registration or to change a classification shall be accompanied by the reasons (including the factual basis) for the action.

(b) Amendments to contents of denials and notices. Such documents under this section may be amended or enlarged by the Administrator at any time prior to the commencement of the public hearing. If the Administrative Law Judge determines that additional time is necessary to permit a party to prepare for matters raised by such amendments, the commencement of the hearing shall be delayed for an appropriate period.