49 C.F.R. § 1300.3
Where a shipper or a prospective shipper or person acting on behalf of a shipper or a prospective shipper requests that the carrier establish a rate in the absence of an existing rate for particular transportation, the carrier must promptly establish and provide to the requester a rate and applicable service terms. The information may be provided either in written or electronic form, as agreed to by the parties. If the parties cannot agree, such information is to be provided in electronic (non-passive) form where both parties have the requisite capabilities; otherwise, it is to be provided in writing. The response should be provided as soon as reasonably possible, but no later than 10 business days from receipt of the request. If a carrier determines that additional information is required from the requester before a rate or term can be established, the carrier must so notify the requester as soon as possible, but no later than 10 business days after receipt of the request. Once the additional information is received, the carrier must set the rate and related service terms, and relay them to the requester, as soon as reasonably possible, but no later than 10 business days from the receipt of the additional information. (However, the parties may agree to a different time period, in which case these time periods would not apply.) A rail carrier may, at its option, require that requests submitted under this section be in written or electronic form, although the carrier may permit oral requests.
49 C.F.R. §1300.3