42 CFR § 489.21 - Specific limitations on charges.
Except as specified in subpart C of this part, the provider agrees not to charge a beneficiary for any of the following:
(a) Services for which the beneficiary is entitled to have payment made under Medicare.
(b) Services for which the beneficiary would be entitled to have payment made if the provider—
(1) Had in its files the required certification and recertification by a physician relating to the services furnished to the beneficiary;
(2) Had furnished the information required by the intermediary in order to determine the amount due the provider on behalf of the individual for the period with respect to which payment is to be made or any prior period;
(3) Had complied with the provisions requiring timely utilization review of long stay cases so that a limitation on days of service has not been imposed under section 1866(d) of the Act (see subpart K of part 405 and part 482 of this chapter for utilization review requirements); and
(4) Had obtained, from the beneficiary or a person acting on his or her behalf, a written request for payment to be made to the provider, and had properly filed that request. (If the beneficiary or person on his or her behalf refuses to execute a written request, the provider may charge the beneficiary for all services furnished to him or her.)
(c) Inpatient hospital services furnished to a beneficiary who exhausted his or her Part A benefits, if CMS reimburses the provider for those services.
(d) Custodial care and services not reasonable and necessary for the diagnosis or treatment of illness or injury, if—
(1) The beneficiary was without fault in incurring the expenses; and
(2) The determination that payment was incorrect was not made until after the third year following the year in which the payment notice was sent to the beneficiary.
(e) Inpatient hospital services for which a beneficiary would be entitled to have payment made under Part A of Medicare but for a denial or reduction in payments under regulations at § 412.48 of this chapter or under section 1886(f) of the Act.
(f) Items and services furnished to a hospital inpatient (other than physicians' services as described in § 415.102(a) of this chapter or the services of an anesthetist as described in § 405.553(b)(4) of this chapter) for which Medicare payment would be made if furnished by the hospital or by other providers or suppliers under arrangements made with them by the hospital. For this purpose, a charge by another provider or supplier for such an item or service is treated as a charge by the hospital for the item or service, and is also prohibited.
(h) Items and services (other than those described in § 489.20(s)(1) through (15)) required to be furnished under § 489.20(s) to a resident of an SNF (defined in § 411.15(p) of this chapter), for which Medicare payment would be made if furnished by the SNF or by other providers or suppliers under arrangements made with them by the SNF. For this purpose, a charge by another provider or supplier for such an item or service is treated as a charge by the SNF for the item or service, and is also prohibited.