Bloomberg Law
April 22, 2020, 10:01 AM

High Court’s Default Test for Proving Job Bias Remains Murky

Robert Iafolla
Robert Iafolla

The U.S. Supreme Court recently handed down a pair of rulings that cemented its view on the default standard for proving workplace bias, but legal scholars say some confusion remains about what that test requires and how difficult it is for workers to meet.

The high court has said workers must show that they wouldn’t have been fired or suffered some other adverse employment action except for their employer’s bias, unless Congress included specific language in a statute that justifies applying a different standard.

That test—known as “but-for causation”—represents a higher bar than the standard favored by worker advocates and plaintiffs’ attorneys, which holds that discrimination is one of potentially several motivating factors.

Having set but-for causation as the default, the court will likely continue going law-by-law to decide whether it applies to the Americans with Disabilities Act, the Family and Medical Leave Act, and the Rehabilitation Act, discrimination law scholars said.

The high court already has an ADA petition teed up. The justices will consider on Friday whether to hear a case brought by a doctor who says he was fired because of the post-traumatic stress disorder he acquired during his military service.

“Now we have a spectrum of standards, but it’s important to emphasize that but-for causation isn’t an extremely onerous standard,” said Sandra Sperino, a University of Cincinnati law professor who’s written extensively on discrimination law. “It only seems onerous if it’s matched up against other standards. In most cases, though, it shouldn’t make a huge difference.”

Comparing tests and labeling but-for causation as strict, and motivating factor as lenient, could be causing some of the confusion in the lower courts, which sometimes have a problem understanding that there can be multiple but-for causes, Sperino said.

Trial and appellate courts have incorrectly equated a but-for cause with being the sole cause, Sperino said. Courts have also misapplied but-for causation when an adverse employment action involved multiple people or stemmed from both legitimate and biased reasons, she said.

But-For Default

After heavy litigation that produced several high court rulings, workers and employers are on notice that workers win discrimination lawsuits if they show bias is:

Last month, the justices unanimously said in Comcast v. National Association of African American-Owned Media, a Section 1981 race bias case, that the but-for standard is the default rule.

The decision also clarified that workers can use the burden-shifting framework for proving bias through indirect evidence—which was set forth in the high court’s 1973 ruling in McDonnell Douglas v. Green—for claims that require a but-for causation, discrimination law scholars said. That had been an open question, they said.

Earlier this month, the court 8-1 ruled in Babb v. Wilkie that, based on the text of the ADEA, an employer violates the law if age was “a factor” in an employment decision.

But the court went on to rule that workers can only get damages and other remedies if they show that age discrimination was a but-for cause of the employment outcome. The more lenient standard to prove employer liability only allows for injunctions and other forward-looking relief, the court said.

Since most workers sue for damages, but-for causation will be the operative standard for many federal sector age bias cases, legal scholars said.

Neither the Babb nor the Comcast decisions, however, provided much guidance for lower courts as to what’s meant by but-for causation, they said.

Prior Guidance on Causation

Nevertheless, the Supreme Court has made clear that a but-for cause is not the same as the sole cause in cases going back decades, discrimination law scholars said.

For example, the high court made that distinction in its 1976 ruling in McDonald v. Santa Fe Trail Transportation, saying a worker needn’t show that the employer acted only on the basis of race—without regard to alleged work performance problems—to show it was a but-for cause of a discharge.

The court has also given guidance on the standard in criminal and negligence cases.

In 2014, Justice Antonin Scalia likened it to the “straw that broke the camel’s back” in a criminal case on enhanced penalties under the Controlled Substances Act.

“Thus, if poison is administered to a man debilitated by multiple diseases, it is a but-for cause of his death even if those diseases played a part in his demise, so long as, without the incremental effect of the poison, he would have lived,” Scalia wrote.

Chief Justice John Roberts criticized but-for causation as being too lenient a standard for proving certain negligence claims in his dissent to a 2011 Federal Employers Liability Act ruling. Roberts used the hypothetical example of assigning liability for a bicyclist crashing because they hit a cone around a construction project to repair a sidewalk damaged after Roberts dropped a piano on it.

“My negligence was a ‘but for’ cause of the injury: If I had not dropped the piano, the bicyclist would not have crashed,” Roberts wrote.

Despite this guidance, some courts still conflate a but-for cause with the sole cause. The U.S. Court of Appeals for the District of Columbia, for example, threw out a worker’s Title VII retaliation claim in a 2015 decision because he couldn’t prove that retaliatory animus was the only cause of an adverse employment action.

‘Grossly Unfair’ Test?

The way that worker advocates have characterized but-for causation has driven some of the confusion over what’s required under that standard, said Katie Eyer, a discrimination law professor at Rutgers University.

Although it’s the nature of advocacy to attack an adversary’s position by stressing the problems it could create, some of the rhetoric about but-for causation being excessively burdensome has been inaccurate, Eyer said. In particular, it’s simply wrong to equate a-but for cause with the sole cause, she said.

The pending Supreme Court petition filed by the former Mayo Clinic doctor appears to engage in some of that hyperbolic rhetoric. Michael Murray is challenging a Ninth Circuit decision that applied but-for causation to the ADA, which he said created a “grossly unfair imbalance” for disability bias lawsuits.

“The disabled plaintiff faces the virtually impossible task of attributing the employer’s conduct to the plaintiff’s disability status, to the exclusion of all other causes, while the employer is permitted simply to ignore the disability and offer up any number of reasons for termination,” Murray’s petition said.

Murray and the Mayo Clinic disagree on whether federal appeals courts are truly split over the ADA’s causation standard, or whether the Supreme Court’s but-for precedent is merely working its way through courts.

Attorneys for Murray and the Mayo Clinic didn’t respond to requests for comment.

On Monday, the Supreme Court rejected a petition asking it to consider the causation standard in the Rehabilitation Act, which prohibits disability bias in the federal government and programs receiving federal aid. That law uses the same causation standard as the ADA section that broadly bars discrimination in employment.

But that denial doesn’t necessarily say anything about the chances that the court will take Murray’s petition, said Michael Foreman, a law professor and director of Penn State University’s Civil Rights Appellate Clinic. Foreman, who represented the worker in the denied Rehabilitation Act petition, said the court may be more interested in taking a straight ADA case.

To contact the reporter on this story: Robert Iafolla in Washington at

To contact the editors responsible for this story: Jay-Anne B. Casuga at; Karl Hardy at