Employees who feel so harassed that they have no choice but to quit can still sue. Cut your liability for what’s known as constructive discharge by transferring the employee.
Recent case: Rosina alleged that her co-workers created a hostile environment. When a co-worker pulled a knife on her, she was immediately transferred. Rosina quit three days later and sued, claiming constructive discharge. The court dismissed her claim, reasoning that she hadn’t given the transfer a chance. (Bennett v. Lew, No. 12-CV-2829, DC MN, 2015)