19 C.F.R. § 10.37
The period of time during which merchandise entered under bond under chapter 98, subchapter XIII, Harmonized Tariff Schedule of the United States (19 U.S.C. 1202 ), may remain in the customs territory of the United States, may be extended for not more than two further periods of 1 year each, or such shorter period as may be appropriate. Extensions may be granted by the Center director upon written application on CBP form 3173, which may be submitted to CBP, either at the port of entry or electronically provided the articles have not been exported or destroyed before the receipt of the application, and liquidated damages have not been assessed under the bond before receipt of the application. Any untimely request for an extension of time for exportation shall be referred to the Director, Commercial and Trade Facilitation Division, Office of International Trade, CBP Headquarters, for disposition. Any request for relief from a liquidated damage assessment in excess of a Fines, Penalties, and Forfeitures Officer's delegated authority shall be referred to the Director, Border Security and Trade Compliance Division, Office of International Trade, CBP Headquarters, for disposition. No extension of the period for which a carnet is valid shall be granted.
19 C.F.R. §10.37