California Code, Labor Code - LAB § 3751

(a) No employer shall exact or receive from any employee any contribution, or make or take any deduction from the earnings of any employee, either directly or indirectly, to cover the whole or any part of the cost of compensation under this division.  Violation of this subdivision is a misdemeanor.

(b) If an employee has filed a claim form pursuant to Section 5401, a provider of medical services shall not, with actual knowledge that a claim is pending, collect money directly from the employee for services to cure or relieve the effects of the injury for which the claim form was filed, unless the medical provider has received written notice that liability for the injury has been rejected by the employer and the medical provider has provided a copy of this notice to the employee.  Any medical provider who violates this subdivision shall be liable for three times the amount unlawfully collected, plus reasonable attorney's fees and costs.