In the 1994 case of Christine McKennon vs. Nashville Banner Publishing Company, the U.S. Supreme Court ruled that an employer cannot use evidence of wrongdoing discovered after an employee's dismissal as a legal defense against a wrongful termination claim if it was initially unaware of this misconduct at the time of firing. The plaintiff, Christine McKennon, had been fired from her job due to alleged age discrimination and later during litigation process, it was found out she had engaged in misconduct (removing confidential documents) while employed. The company argued that even if they did fire her because of her age originally (which they denied), they would have fired her anyway once discovering this misconduct thus making their initial reason irrelevant. However, Justice Anthony Kennedy writing for unanimous court disagreed stating that allowing such after-acquired evidence to absolve companies completely could potentially undermine anti-discrimination laws by encouraging post-termination investigations aimed at digging up dirt on dismissed employees.

In the dissenting opinion for Christine McKennon v. Nashville Banner Publishing Company, Justice Scalia argued that the majority's decision was not in line with the Age Discrimination in Employment Act (ADEA). He believed that this law did not provide a remedy for unlawful termination when an employer later discovers misconduct that would have led to firing anyway. According to him, it is irrelevant whether or not an employer had knowledge of any wrongdoing at the time of dismissal because if they discover such behavior afterwards, they should be able to use it as a legitimate reason for termination. Therefore, he disagreed with the majority's view that employers could still face liability even after uncovering post-termination evidence of employee misconduct which would have justified dismissal on its own.