In Palmquist v. Shinseki, the U.S. Court of Appeals for the First Circuit held that a disabled employee who alleged that his employer failed to promote him because he complained of disability-based discrimination was required to establish that his complaint was the "but-for" reason why he was not promoted, and not merely a motivating factor.

Mark Palmquist, a veteran who suffered a brain injury during his military service, brought a retaliation claim against his employer, the Department of Veterans Affairs. Since Palmquist was employed by a federal government agency, he brought his claim under the Rehabilitation Act of 1973, which prohibits federal government agencies from discriminating against employees on the basis of disability or retaliating against them for raising discrimination complaints.

After unsuccessfully applying for a promotion, Palmquist complained to his employer that he did not receive the promotion preferences to which he was entitled under federal law as a disabled veteran. Palmquist subsequently applied for another promotion, and his supervisor gave a reference in which she made remarks arguably related to Palmquist's earlier complaints, such as saying that Palmquist tends to "go overboard" on behalf of veterans. While the supervisor said that she intended those comments to reflect positively on Palmquist, the decision-maker viewed the comments negatively and did not give Palmquist the promotion.

Palmquist alleged that his employer denied him the promotion because of his complaints and, in so doing, unlawfully retaliated against him. At trial, the jury found that while Palmquist's complaints were a motivating factor in the decision not to promote him, the complaints were not the "but-for" cause of that decision. The trial court therefore entered judgment for the employer.

Palmquist appealed to the First Circuit, arguing that the trial court should have entered judgment in his favor because the jury found that his complaints were a motivating factor in the decision not to promote him. The First Circuit rejected this argument, holding that Palmquist had to establish that his complaints were the "but-for" cause of his employer's decision. The First Circuit reasoned that Congress amended Title VII, which prohibits discrimination on the basis of factors such as race, to allow a plaintiff to prove a violation by establishing that a protected characteristic was a motiving factor in an employment decision, even if it was not the "but-for" cause. Congress, however, did not make a similar amendment to the Americans with Disabilities Act (ADA), which is the statute that courts review when addressing Rehabilitation Act claims. The ADA, like the Age Discrimination in Employment Act (ADEA), states that no person shall retaliate against an individual "because" the individual has opposed any discriminatory practices. The U.S. Supreme Court held that the ADEA requires proof of but-for causation.

While Palmquist's claim was brought under the Rehabilitation Act, which does not apply to most private employers, the First Circuit's decision is significant to private employers because the Rehabilitation Act borrows its causation standard from the ADA. Employers can argue therefore that under the ADA an employee must establish "but-for" causation and that motivating factor causation is insufficient.