31 C.F.R. § 309.1
The Secretary of the Treasury is authorized by the Second Liberty Bond Act, as amended, to issue Treasury bills of the United States on an interest-bearing basis, on a discount basis, or on a combination interest-bearing and discount basis, at such price or prices and with interest computed in such manner and payable at such time or times as he may prescribe; and to fix the form, terms, and conditions thereof, and to offer them for sale on a competitive or other basis, under such regulations and upon such terms and conditions as he may prescribe. Pursuant to said authorization, the Secretary of the Treasury may, from time to time, by public notice, offer Treasury bills for sale, and invite tenders therefor, through the Federal Reserve Banks and branches and through the Department of the Treasury, Bureau of the Fiscal Service. The Treasury bills so offered, and the tenders made, will be subject to the terms and conditions and to the general rules and regulations herein set forth, except as they may be modified in the public notices issued by the Secretary of the Treasury in connection with particular offerings.
31 C.F.R. §309.1