D.C. Code § 1-204.66

General obligation bonds issued under this part may be sold at a private sale on a negotiated basis (in such manner as the Mayor may determine to be in the public interest), or may be sold at public sale upon sealed proposals after publication of a notice of such public sale at least once not less than 10 days prior to the date fixed for sale in a daily newspaper carrying municipal bond notices and devoted primarily to financial news or to the subject of State and municipal bonds published in the city of New York, New York, and in one or more newspapers of general circulation published in the District. Such notice of public sale shall state, among other things, that no proposal shall be considered unless there is deposited with the District as a down payment a certified check, cashier’s check, or surety for an amount equal to at least 2% of the par amount of general obligation bonds bid for, and the Mayor shall reserve the right to reject any and all bids.