48 CFR §9.104-4

1. (a)Generally, prospective prime contractors are responsible for determining the responsibility of their prospective subcontractors (but see 9.405 and 9.405-2 regarding debarred, ineligible, or suspended firms). Determinations of prospective subcontractor responsibility may affect the Government's determination of the prospective prime contractor's responsibility. A prospective contractor may be required to provide written evidence of a proposed subcontractor's responsibility.
2. (b)When it is in the Government's interest to do so, the contracting officer may directly determine a prospective subcontractor's responsibility (e.g., when the prospective contract involves medical supplies, urgent requirements, or substantial subcontracting). In this case, the same standards used to determine a prime contractor's responsibility shall be used by the Government to determine subcontractor responsibility.