Cal. Lab. Code § 2801
In any action to recover damages for a personal injury sustained within this State by an employee while engaged in the line of his duty or the course of his employment as such, or for death resulting from personal injury so sustained, in which recovery is sought upon the ground of want of ordinary or reasonable care of the employer, or of any officer, agent or servant of the employer, the fact that such employee has been guilty of contributory negligence shall not bar a recovery therein where his contributory negligence was slight and that of the employer was gross, in comparison, but the damages may be diminished by the jury in proportion to the amount of negligence attributable to such employee.
It shall be conclusively presumed that such employee was not guilty of contributory negligence in any case where the violation of any law enacted for the safety of employees contributed to such employee's injury.
It shall not be a defense that:
No contract, or regulation, shall exempt the employer from any provisions of this section.
Ca. Lab. Code § 2801