22 U.S.C. § 286p

(a) The Secretary of the Treasury is authorized to issue to the Federal Reserve banks, and such banks shall purchase, Special Drawing Right certificates in such form and in such denominations as he may determine, against any Special Drawing Rights held to the credit of the Exchange Stabilization Fund. Such certificates shall be issued and remain outstanding only for the purpose of financing the acquisition of Special Drawing Rights or for financing exchange stabilization operations. The amount of Special Drawing Right certificates issued and outstanding shall at no time exceed the value of the Special Drawing Rights held against the Special Drawing Right certificates. The proceeds resulting from the issuance of Special Drawing Right certificates shall be covered into the Exchange Stabilization Fund. (b) Special Drawing Right certificates owned by the Federal Reserve banks shall be redeemed from the resources of the Exchange Stabilization Fund at such times and in such amounts as the Secretary of the Treasury may determine.