The employer is automatically liable for harassment by a supervisor that results in a negative employment action such as termination, failure to promote or hire, and loss of wages. If the supervisor’s harassment results in a hostile work environment, the employer can avoid liability only if it can prove that: 1) it reasonably tried to prevent and promptly correct the harassing behavior; and 2) the employee unreasonably failed to take advantage of any preventive or corrective opportunities provided by the employer.
The employer will be liable for harassment by non-supervisory employees or non-employees over whom it has control (e.g., independent contractors or customers on the premises), if it knew, or should have known about the harassment and failed to take prompt and appropriate corrective action.
via Harassment.