Any physician who makes or causes to be made a referral prohibited by this part is in violation of the medical practice law, as compiled in this chapter. Willful violations of this part are considered unprofessional conduct, which conduct is subject to licensure sanction by the board of medical examiners, including suspension, revocation or other restriction deemed appropriate by the board. In addition, the board is authorized to impose civil penalties of an amount up to five thousand dollars ($5,000) for each prohibited referral.