Treas. Reg. § 54.9816-6A

(a) In general. When providing any remittance advice (including in paper or electronic form) to an entity (other than a participant, beneficiary, or enrollee) that does not have a contractual relationship, directly or indirectly, with a group health plan or a health insurance issuer offering group or individual health insurance coverage for the furnishing of an item or service under the plan or coverage, in response to a claim for payment for health care items and services furnished by that entity, the plan or issuer must use claim adjustment reason codes (CARCs) and remittance advice remark codes (RARCs) (as those terms are described in standards and operating rules adopted at 45 CFR part 162) in the manner and timeframe specified in guidance issued by the Secretaries of the Treasury, Labor, and Health and Human Services, or as required under any applicable adopted standards and operating rules under 45 CFR part 162, to communicate information related to whether the claim is or is not subject to the provisions of this part and 45 CFR 149 subparts E and F.

(b) Severability