12 U.S. Code § 2285 - Functions
(a) Purchase and sale of obligations issued, sold, or guaranteed by Federal agencies
The Bank is authorized to make commitments to purchase and sell, and to purchase and sell on terms and conditions determined by the Bank, any obligation which is issued, sold, or guaranteed by a Federal agency. Any Federal agency which is authorized to issue, sell, or guarantee any obligation is authorized to issue or sell such obligations directly to the Bank.
Any purchase by the Bank shall be upon such terms and conditions as to yield a return at a rate not less than a rate determined by the Secretary of the Treasury taking into consideration
(1) the current average yield on outstanding marketable obligations of the United States of comparable maturity, or
(2) whenever the Bank’s own obligations outstanding are sufficient, the current average yield on outstanding obligations of the Bank of comparable maturity.