5 C.F.R. § 919.400
May I enter into a transaction with an excluded or disqualified person?
(a) You as an agency official may not enter into a covered transaction with an excluded person unless you obtain an exception under § 919.120.
(b) You may not enter into any transaction with a person who is 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.