2 C.F.R. § 180.400
May I enter into a transaction with an excluded or disqualified person?
(a) As a Federal agency official, you may not enter into a covered transaction with an excluded person unless you obtain an exception under § 180.135.
(b) You may not enter into any transaction with a person disqualified from that transaction unless you obtain a waiver or exception under the statute, Executive Order, or regulation that is the basis for the person's disqualification.