As a condition of participation in the medical assistance program, vendors of services shall agree to accept the rates of payment authorized by this article and shall not seek nor accept additional payments. The department shall permit each person eligible for assistance under this act freedom to choose whichever practitioner and/or vendor of the services, care or prescribed drugs he shall desire so long as such practitioner or vendor is entitled to participate in the assistance program provided for in this act.
62 P.S. § 444.1