California Code of Regulations
Title 8 - Industrial Relations
Division 1 - Department of Industrial Relations
Chapter 3.2 - California Occupational Safety and Health Regulations (Cal/OSHA)
Subchapter 2 - Regulations of the Division of Occupational Safety and Health
Article 1 - Employers' Obligation to Provide Information to Employees
Section 340.2 - Notification to Employee of Exposure Required

Whenever any employee has been or is being exposed to toxic materials or harmful physical agents in concentrations or at levels exceeding those prescribed by applicable standard, order, or special order, the employer of the affected employee must promptly notify any employee so affected in writing of the fact that the employee has been exposed, and of the corrective action being taken by the employer.