2 C.F.R. § 180.305
May I enter into a covered transaction with an excluded or disqualified person?
(a) As a participant, you may not enter into a covered transaction with an excluded person unless the Federal agency responsible for the transaction grants an exception under § 180.135.
(b) You may not enter into any transaction with a person who is disqualified from that transaction unless you have obtained an exception under the disqualifying statute, Executive Order, or regulation.