Does quid pro quo sexual harassment apply to employee-employee conduct?

Generally, only employees with the authority to impact a tangible employment benefit, such as hiring, firing, promoting, reassigning to another position with different responsibilities, or monetary benefits, can be held liable for engaging in quid pro quo sexual harassment. 

In the ordinary case, this is limited to supervisors and managers. However, if an employee has de facto authority of this type, the employer can still be held liable. For example, if the owner's son is merely a co-worker of an employee he is sexually harassing, he would likely still be considered to have authority sufficient enough to hold him liable for quid pro quo harassment. However, if the employer knows that a co-worker is demanding sexual favors from another worker and does nothing about it, the employer would probably be liable for sexual harassment due to the hostile environment.