A payor who is required to withhold under § 31.3406(a)-1 must withhold—

(a) On the accounts subject to withholding under § 31.3406(a)-1 (b)(1)(i) or (b)(2)(ii); and

(b) On the accounts subject to withholding under § 31.3406(a)-1(b)(1)(ii) or (b)(2)(i), as described under § 31.3406(d)-5 (relating to notification of incorrect TIN) or § 31.3406(c)-1 (relating to notified payee underreporting), respectively.