Raytheon v. Hernandez, decided by the U.S. Supreme Court in 2003, confirmed that an employer may lawfully refuse to rehire a previously terminated employee as long as the refusal is based on a neutral no-rehire policy and not on some protected trait. Today's South Jersey Courier Post talks about the benefits to employers to rehiring former employees who left on good terms, so called "boomerang" employees:
[A]s the marketplace becomes more globally competitive for skilled workers, companies find that it makes perfect sense to rehire former workers.... No longer is it seen as disloyal for an employee to go to another company for career opportunities, and employers are welcoming back former workers with open arms.
In rehiring a former employee, consideration must be paid to whether that specific rehiring decision will make a decision not to rehire another employee appear discriminatory. It may make perfect business sense to rehire one employee and not another, but if the rehired employee is outside a protected class, it may cause the rejection of other former employees to be questioned. If you have a blanket no rehire policy, it is best to either follow it, or be prepared to explain why you chose not to follow it in a specific instance. If you instead choose to rehire ex-employees on a case by case basis, make sure to have a legitimate business reason why one employee's request was granted and not another's.