47 C.F.R. § 213.5 – Precedence designators.

(a) The following precedence designators are available for Government and public correspondence users:
Federal Government Domestic public correspondence and international telephone calls
Flash Flash emergency.
Immediate Immediate emergency.
Priority Priority emergency.
Routine (No domestic equivalent.)
(b) Government and non-Government users of public correspondence services will handle their international messages in accordance with current ITU Telegraph Regulations. Government users should note that, generally, the only precedence designator available for their use for international messages sent over public correspondence circuits if Etat Priorite. The ITU Regulations do not contain precedence designators which equate to Flash, Immediate, or Priority. Accordingly, Government messages whether Flash, Immediate, or Priority precedence when sent over international public correspondence circuits will be handled as Etat Priorite messages. Thus, Priority messages will receive the same treatment in transmission and processing as Immediate or Flash messages. Conversely, Etat Priorite messages received in the United States shall be transmitted and processed in the order of receipt, to the extent possible. The precedence designator available for non-Government users of public correspondence services is Urgent. The Urgent designator is limited for use only during wartime conditions, as declared pursuant to section 606 of the Communications Act of 1934.
(c) Domestic and International U.S. common carriers, insofar as practicable by agreement with their foreign correspondents, shall endeavor to arrange the proper level of precedence handling of international messages and calls originating, terminating in, or transiting the United States: Provided, however, That insofar as international messages are concerned the level of precedence shall be consistent with the International Telecommunication Conventions and regulations thereunder.
(d) The Government designators shall be used throughout the Federal Government. All messages and telephone calls sent via public correspondence services shall use domestic or international public correspondence designators as appropriate. Thus, the responsibility is on Government and public correspondence users to recognize and use the appropriate designators when using public correspondence services.
(e) On international telephone calls the carrier's operator will convert to the appropriate international designator.

Federal Government	Domestic public correspondence and international telephone calls
Flash	Flash emergency.
Immediate	Immediate emergency.
Priority	Priority emergency.
Routine	(No domestic equivalent.)