In the case of Jack Gross v. FBL Financial Services, Inc., the U.S Supreme Court was tasked with determining whether a plaintiff must present direct evidence of age discrimination to obtain a mixed-motives instruction in a suit brought under the Age Discrimination in Employment Act (ADEA). The court ruled that plaintiffs must prove by preponderance of evidence that age was the "but-for" cause for their employer's adverse action. This decision effectively raised the burden of proof for plaintiffs claiming age discrimination under ADEA compared to those alleging other forms of workplace bias. The ruling also clarified that unlike Title VII cases where an unlawful motive need only be a motivating factor, not necessarily decisive one, ADEA requires proof that discriminatory intent had determinative influence on outcome. In this specific case, Gross claimed he was demoted due to his age and while lower courts initially sided with him based on jury instructions allowing them to find for Gross if he proved his demotion would not have occurred but-for his employer’s motive to discriminate against him because of his age; however, upon appeal it went up all way up to Supreme Court which reversed previous rulings stating they misinterpreted precedent regarding burden-shifting frameworks.

In the dissenting opinion for Gross v. FBL Financial Services, Inc., Justice John Paul Stevens argued that the majority's decision to require plaintiffs in age discrimination cases to prove that age was the decisive factor in their adverse employment action was a departure from precedent and an unnecessary burden on victims of discrimination. He contended that previous rulings had allowed mixed-motive claims under similar anti-discrimination laws, where plaintiffs only needed to show that illegal bias was one motivating factor among others. The justice also criticized the majority for ignoring congressional intent behind Age Discrimination in Employment Act (ADEA), which he believed aimed at eradicating all forms of discriminatory treatment based on age rather than just those where it is proven as a sole cause. Furthermore, he expressed concern over how this ruling could potentially affect future interpretations of other civil rights statutes with similar language.