Labor Code § 4056
CHAPTER 7. Medical Examinations
No compensation is payable in case of the death or disability of an employee when his death is caused, or when and so far as his disability is caused, continued, or aggravated, by an unreasonable refusal to submit to medical treatment, or to any surgical treatment, if the risk of the treatment is, in the opinion of the appeals board, based upon expert medical or surgical advice, inconsiderable in view of the seriousness of the injury.