In the vast majority of circumstances the parties are able to reach agreement. Should they be unable to reach an agreement on appropriate mitigation for a MOA or project PA, there are certain alternative courses of action. If the SHPO terminates consultation, then the agency and the ACHP can consult and may execute an agreement without the SHPO. If a THPO or Indian tribe terminates consultation regarding an undertaking occurring on or affecting tribal lands, the agency and the ACHP cannot execute an agreement, and the ACHP shall comment pursuant to 36 CFR § 800.7.

Where the agency and the SHPO/THPO cannot agree on the terms of the agreement, the agency official shall request the ACHP to join the consultation (if it is not already participating) and provide to the ACHP the documentation specified in 36 CFR § 800.11(g). If the ACHP decides to join the consultation, the agency shall proceed to consult further with the SHPO/THPO, ACHP, and any other consulting parties to reach agreement. If the ACHP elects not to join the consultation, it shall notify the agency and proceed to comment in accordance with 36 CFR § 800.7(c).

Where the ACHP is already participating in the consultation and the agency terminates consultation, the head of the agency or the assistant secretary or other officer with major department-wide or agency-wide responsibilities shall request the ACHP comment pursuant to 36 CFR § 800.7(c), and shall notify all consulting parties of this request.

If the ACHP terminates consultation, the ACHP shall notify the agency official, the agency's Federal Preservation Officer (FPO), and all consulting parties and proceed to comment in accordance with 36 CFR § 800.7(c). The ACHP may consult with the agency's FPO prior to terminating consultation to seek to resolve issues concerning the undertaking and its effects on historic properties. Further, when the ACHP issues formal comments, they represent the comments of its Presidentially and statutorily designated members, not the staff.

When the consulting parties cannot reach agreement on the terms of a program PA, the agency must use the standard Section 106 process for each individual undertaking that would have been covered by the program PA.