CA Business & Professions Code §511.1(c)

Beginning July 1, 2000, a payor, as defined in subparagraph (B) of paragraph (3) of subdivision (d), shall do all of the following: (1) Provide an explanation of benefits or explanation of review that identifies the name of the plan or network that has a written agreement signed by the provider whereby the payor is entitled, directly or indirectly, to pay a preferred rate for the services rendered.