49 CFR 172.604 defines the requirements for the inclusion of Emergency Response Phone Numbers on Hazardous Waste Manifests (HWM). At times though, there can be some ambiguity and confusion as to when a contract number needs to appear along with the ER Phone number on HWMs.
We know that the HWM functions as the USDOT Hazardous Material (HM) Shipping paper. It is also clear that USDOT requires that an Emergency Response Phone Number appears on the HM Shipping Paper and that the phone number must connect to someone, an actual person (not a computer operator) that has knowledge regarding the HM being shipped at that time in any mode. Many Hazardous Waste Generators contract that service out to an Emergency Response Information (ERI) provider such as Chemtrec. In such cases, we know that the ERI provider requires a contract, typically with the shipper, and that the shipper is responsible for furnishing the ERI provider with all of the pertinent information regarding any HM that is offered for shipping. In some cases a 3rd party may have the actual contract with the ERI provider and not the actual shipper of record. The 3rd party is then responsible for providing the HM information to the ERI provider.
Confusion then can arise regarding if and when the Contract Number, usually in association with the ERI Phone Number, itself also needs to appear on the shipping paper. It is important in these situations to consider who has the actual contract with the ERI. Is it the actual shipper listed on the shipping paper or is it a 3rd party? In instances where the contract is with the actual shipper identified on the shipping paper, the contract number with the ERI need not appear on the Shipping Paper. It is permissible to include the contract number here, but it is not required.
Consider this guidance from Chemtrec: “If your shipment is subject to U.S. shipping regulations, your registered company name or your CHEMTREC CCN should be entered, in accordance with 49 CFR 172.604, on the shipping paper immediately before, after, above, or below the emergency response telephone number in a prominent, readily identifiable, and clearly visible manner that allows the information to be easily and quickly found, unless the company name is entered elsewhere in a prominent manner.” 
This guidance from USEPA specific to HWMs is also good to keep in mind: “First, if the generator/offeror is the original generator/offeror that contracted with the ERI provider, and the generator’s or offeror’s name is displayed in Item 5 (Generator’s Name and Mailing Address) of the manifest, then no additional information need be included on the manifest to satisfy the requirements of the DOT rule. Since the original generator/offeror entity that contracted with the ERI provider is already identified clearly in Item 5, this information does not need to be repeated elsewhere on the form.”
Therefore, as along as the shipper/generator/offeror has made the contractual arrangements with the ERI provider, just the ER Phone Number needs to appear in section 3 of the HWM. In those cases where a third party holds the contract with the ERI provider and provides the HM info to the ERI provider, the contract number must appear on the shipping paper, along with the ER phone number. This helps the ERI provider by tying the HM being shipped to the contract & to the provider of the HM information.