On June 18, 2009, in Gross v. FBL Financial Services, Inc., the United States Supreme Court rejected the notion that an age discrimination plaintiff may use the so-called "mixed motive" theory to require the defendant to prove that it would have taken the challenged action regardless of age. The Court held instead that a plaintiff asserting a claim under the Age Discrimination in Employment Act (ADEA) must prove that age was the "but-for" cause of the employer's adverse employment action.

In so deciding, the Court distinguished the burden-shifting analysis of Title VII claims from the analysis required under ADEA. By highlighting the differences in analysis under these two prominent federal statutes, the Court has signaled ADEA plaintiffs will not get the benefit of the "mixed motive" analysis that is available under Title VII.

This case arose when, in 2003, the plaintiff, Jack Gross, was 54 years old, and his employer, FBL Financial Services, Inc. ("FBL"), reassigned him to a new position. FBL also transferred many of Gross's former job responsibilities to a newly created position, awarded to an employee in her early forties whom Gross had previously supervised. Gross sued FBL under the ADEA, which makes it unlawful for an employer to take adverse action against an employee "because of such individual's age."

At trial, Gross introduced evidence suggesting that his reassignment was based at least in part on his age. FBL defended its decision on the grounds that Gross's reassignment was part of a corporate restructuring and that Gross's new position was better suited to his skills. Over FBL's objections, the District Court instructed the jury on the "mixed motive" burden of persuasion used in Title VII cases set forth in Price Waterhouse v. Hopkins, 490 U.S. 228 (1989). The instruction required Gross to prove his age was "a motivating factor" in FBL's decision, and if successful, the burden shifted to FBL to establish that it "would have demoted [Gross] regardless of his age." The jury returned a verdict for Gross.

On appeal in the Eighth Circuit, the Court of Appeals reversed, concluding that the District Court erroneously had given a "mixed motive" jury instruction because Gross had failed to present any "direct evidence" of discrimination, which it interpreted Price Waterhouse to require.

The Supreme Court took a different view than the courts below, holding the "mixed motive" analysis - which was first introduced for use in Title VII cases - is not applicable to cases under the ADEA. The Court based its decision primarily on the textual differences between Title VII and the ADEA, as well as Congress's amendment of Title VII as part of the Civil Rights Act of 1991 and the absence of such an amendment to ADEA.

As a result of the 1991 amendments, Title VII explicitly authorizes discrimination claims in which an improper consideration was "a motivating factor" for an adverse employment decision. See 42 U.S.C. §2000e-2(m). The ADEA provides, on the other hand, that "[i]t shall be unlawful for an employer...to...discriminate against any individual...because of such individual's age." 29 U.S.C. §623(a)(1) (emphasis added). Taking the ordinary, dictionary meaning of the term "because of" - i.e., "by reason of" or "on account of" - the Court concluded that a plaintiff suing under the ADEA must prove that age was the "but-for" cause of the employer's adverse decision.

The Court's adherence to the "but-for" causation standard, and rejection of the "mixed motive" analysis in ADEA cases, is more than a matter of semantics for employers defending claims of age discrimination. By eliminating the potential for the burden of proof to shift to a defendant in an ADEA case, the Court's decision will make it more difficult for plaintiffs to prevail where there is evidence that age was one of the reasons for the challenged adverse action.