So-called “mixed motive” cases, where there is evidence of unlawful bias but also evidence of a legitimate, nondiscriminatory reason for an employment action, have generated a great deal of debate over the applicable burden of proof. In 1989, a divided U.S. Supreme Court held in Price Waterhouse v. Hopkins that, once a plaintiff has proven that unlawful animus was “a motivating factor” in an employment decision, the burden of proof shifts to the defendant to prove that it would have taken the same action even absent the unlawful animus. This approach was essentially ratified by Congress when it approved certain amendments to Title VII in enacting the Civil Rights Act of 1991. But, because Price Waterhouse applied to a claim under Title VII, and federal age discrimination claims fall under the Age Discrimination in Employment Act (ADEA), which was not similarly amended by the Civil Rights Act of 1991, the burden of proof applicable to mixed-motive ADEA cases has remained in dispute.

On June 18, 2009, the U.S. Supreme Court resolved this dispute in Gross v. FBL Financial Services, holding that the burden of proof for an ADEA claim remains with the plaintiff at all times, even in a mixed-motive case. The Court’s 5-4 decision relied heavily on the differences in statutory framework between the ADEA and Title VII in distinguishing the result in Price Waterhouse. The majority opinion, written by Justice Thomas, pointed out that the ADEA required the plaintiff to prove that he was demoted “because of” his age and that there is no statutory basis to shift the burden of proof to the defendant simply because the plaintiff produced some evidence that age was one motivating factor in the decision. The plaintiff still retained the burden of proof to demonstrate that he would not have been demoted “but for” his age.

With Congress all too willing these days to enact legislation overturning employment law decisions of the Supreme Court that displease it, it will interesting to see how long the holding in Gross stands.