19 C.F.R. § 177.5
Each person submitting a request for a ruling in connection with a Customs transaction shall immediately advise Customs in writing of any change in the status of that transaction, as defined in § 177.1(d)(3) . In particular, the Customs Service office to which the request was made must be advised when any transaction described in the ruling request as prospective becomes current and under the jurisdiction of a Customs Service field office. In addition, any person engaged in a Customs transaction coming under the jurisdiction of a Customs Service field office and having previously requested a ruling with respect to that transaction shall advise the field office of that fact. The field office will normally withhold action with respect to any transaction for which a ruling has previously been requested pending the disposition of the ruling request.
19 C.F.R. §177.5