Payment (usually by doctors or lawyers) of part of the fee in return for the referral WordNet 3.0 & Open English WordNet

Fee splitting is the practice of sharing fees with professional colleagues, such as physicians or lawyers, in return for being sent referrals. Wikipedia

The practice, usually of questionable ethicality, by some professionals, such as medical doctors and lawyers, of sending a client to a second practitioner for an additional consultation in order to obtain another payment from the client or from his or her insurer, and in return for which the original practitioner receives a portion of the payment made to the second practitioner (a "commission" or "piece of the action"). Wiktionary