On June 18, 2009, the U.S. Supreme Court held in Gross v. FBL Financial Services, Inc. that a plaintiff bringing an age discrimination claim under the ADEA must prove, by a preponderance of the evidence, that age was the "but-for" cause of the employer's challenged adverse employment action. Distinguishing claims brought under the ADEA from those brought under Title VII, the Court concluded that, unlike in Title VII cases, the burden of persuasion in an ADEA case does not shift to the employer to show that it would have taken the same action regardless of age, even when a plaintiff has produced some evidence that age was one motivating factor in that decision. Gross thus raises the bar for plaintiffs with age discrimination claims and makes it harder to prove age discrimination than other kinds of discrimination under Title VII, where a plaintiff can prevail by simply proving that discrimination was a motivating factor in the employer's adverse decision.

In a 5-4 opinion, the Gross majority based its decision on the different language of the ADEA and Title VII. It determined that, unlike Title VII, which has been amended to explicitly authorize discrimination claims where an improper consideration was "a motivating factor" for the adverse action, the ADEA does not provide that a plaintiff may establish discrimination by showing that age was simply a motivating factor. The Court found it noteworthy that Congress failed to add such language to the ADEA when it added the motivating factor language to Title VII, even though it contemporaneously amended the ADEA in several other ways -- thus leading the Court to conclude that Congress' omission was intentional.

The implications of the Gross holding may very well reach beyond the confines of the ADEA and require "but-for" proof in other employment discrimination claims not governed by Title VII, such as those brought under Section 1981 and Title IX. In the same vein, Gross potentially undermines mixed-motive retaliation cases under the ADEA and Title VII, where courts have held that the "mixed-motive" language applicable to Title VII discrimination claims does not apply to retaliation claims because of differences in how the anti-retaliation sections are drafted.

However, employers should resist the temptation to get too comfortable with the Gross decision and the resulting heightened standard of proof in age claims. The Gross opinion practically invites Congress to take another crack at the ADEA and include the motivating-factor language found in Title VII to overturn this decision and keep the ADEA in line with Title VII.