If you don’t know an employee has engaged in so-called protected activity, you can’t be liable for retaliation.
Recent case: Tina worked through an employment agency to obtain job assignments. The agency didn’t pay Tina; the assigned workplaces did.
Tina worked in a kitchen at one such employer. She complained to a kitchen supervisor that another supervisor had sexually harassed her. The next morning, the employment agency informed her that she should not return to the assignment, but that it would place her elsewhere. No one at the employment agency knew about the sexual harassment complaint.
Tina sued both the kitchen and the employment agency, alleging retaliation for reporting sexual harassment.
But the employment agency quickly had the case against it dismissed by showing that no one—neither those in the kitchen where Tina had been assigned nor Tina herself—had informed it about the complaint. Since it didn’t know about the complaint, it couldn’t retaliate. (Deeter v. Trinity Services and Miller Brothers Staffing Solutions, No. 14-215E, WD PA, 2015)
Final note: Could the employment agency have been considered a joint employer liable for retaliation? No, because the agency didn’t handle, control the job, discipline Tina or otherwise act as her employer.