17 CFR 1.43: Letters of credit as collateral.

A futures commission merchant shall not accept a letter of credit as collateral unless such letter of credit may be exercised, through its stated date of expiry, under the following conditions, regardless of whether the customer posting that letter of credit is in default in any obligation:

(a) In the event that an order for relief under chapter 7 of the Bankruptcy Code or a protective decree pursuant to section 5(b)(1) of SIPA is entered with respect to the futures commission merchant, or if the FDIC is appointed as receiver for the futures commission merchant pursuant to 12 U.S.C. 5382(a), the trustee for that futures commission merchant (or, as applicable, FDIC) may draw upon such letter of credit, in full or in part, in accordance with § 190.04(d)(3) of this chapter.

(b) If the letter of credit is passed through to a clearing organization, then in the event that an order for relief under chapter 7 of the Bankruptcy Code is entered with respect to the clearing organization, or if the FDIC is appointed as receiver for the clearing organization pursuant to 12 U.S.C. 5382(a), the trustee for that clearing organization (or, as applicable, FDIC) may draw upon such letter of credit, in full or in part, in accordance with § 190.04(d)(3) of this chapter.

(c) A futures commission merchant shall not accept a letter of credit from a customer as collateral if it has any agreement with the customer that is inconsistent with this section.