7 CFR 789.43: Letters of understanding.

(a) A letter of understanding is an official action that may be issued in resolving special priorities assistance cases to reflect an agreement reached by all parties (USDA, the Department of Commerce (if applicable), a delegate agency (if applicable), the supplier, and the customer).

(b) A letter of understanding is not used to alter scheduling between rated orders, to authorize the use of priority ratings, to impose restrictions under this part, or to take other official actions. Rather, letters of understanding are used to confirm production or shipping schedules that do not require modifications to other rated orders.