42 CFR §419.80

1. (a)Basis. The provisions in this subpart are issued under the authority of section 1833(t)(2)(F) of the Act, which authorizes the Secretary to develop a method for controlling unnecessary increases in the volume of covered hospital outpatient department services.
2. (b)Scope. This subpart specifies the process and requirements for prior authorization for certain hospital outpatient department services as a condition of Medicare payment.