(a) At maturity. A certificate may not be called for redemption by the Secretary of the Treasury prior to maturity except when the amount of the unexpended portion of the loan from the Rural Electrification Administration or Rural Telephone Bank is less than the face amount of the certificate. Unless the Treasury has received from the owner, at least one week prior to the maturity date of a certificate, a written request for payment at maturity, it shall automatically redeem the same at maturity, and reinvest in the owner's name the principal amount in a new certificate having the same description in all material respects as the one redeemed. No such automatic reinvestment shall be made, however, in excess of the amount of the unexpended portion of the loan from the Rural Electrification Administration or the Rural Telephone Bank.

(b) Prior to maturity. A certificate may be redeemed prior to maturity at par and accrued interest at the owner's option on one week's notice in writing after one month from the issue date. A certificate issued upon reinvestment, as provided in paragraph (a) of this section, shall not be subject to the one-month holding period. A notice to redeem a certificate prior to its maturity date must be given by the official authorized to redeem it, as shown in the subscription for purchase, to the Bureau of the Fiscal Service, Division of Securities Operations, Washington, DC 20226, by letter or wire.