Rather, the court said in the case of Desert Palace Inc. v. Costa, circumstantial evidence is sufficient.

Employer's groups had urged the court to require direct evidence of discrimination in mixed motive cases.

In a joint brief filed by the Equal Employment Advisory Council and the U.S. Chamber of Commerce, both of Washington, the two major employer's associations said that if direct evidence of discrimination is not required, employers would face significant hurdles when defending themselves against discrimination claims.

Indeed, the groups said, every discrimination claim will be turned into a mixed motive case, shifting the burden to the employer in every instance to prove its employment action was based on legitimate criteria.

"Employers would have to prove their innocence, even if the plaintiff presented only circumstantial evidence of discrimination," the groups said in their brief.

The case involves Catharina Costa, who was employed by Desert Palace?the owner of Caesar's Palace Hotel in Las Vegas?as a warehouse worker and heavy equipment operator. Ms. Costa was the only woman in this job.

Ms. Costa was the subject of several disciplinary actions by Desert Palace. Following a physical altercation with a male co-worker, Ms. Costa was terminated. The co-worker, who had a clean disciplinary action record, received a five-day suspension.

Ms. Costa sued Desert Palace charging sex discrimination, arguing that she received harsher discipline than men for the same conduct. She also argued that she was treated less favorably than men in the assignment of overtime, that her supervisors stacked the disciplinary record against her, that her supervisors tolerated sexual slurs against her, and that she was stalked by one of her supervisors.

The crux of the case involves the instructions given to the jury by the United States District Court judge.

The judge told the jury that if it found that the plaintiff's sex was a motivating factor in the defendant's treatment of the plaintiff, then the plaintiff is entitled to the verdict even if the defendant's conduct was also motivated by a lawful reason.

The judge also told the jury that if it found that the defendant's treatment of the plaintiff was motivated by both gender and lawful reasons, it must decide whether the plaintiff is entitled to damages.

The plaintiff is entitled to damages, the judge said, unless the defendant proves by a preponderance of the evidence that it would have treated the plaintiff similarly even if gender had played no role in the decision.

The jury ruled in favor of the plaintiff.

Desert Palace appealed the jury instruction, arguing that the plaintiff did not provide substantial evidence of discrimination. But after several hearings, the 9th Circuit Court of Appeals upheld both the jury instruction and the award.

In a decision written by Justice Clarence Thomas, the high court unanimously upheld the 9th Circuit's decision.

The underlying statute, the court said, referring to the Civil Rights Act of 1964, unambiguously states that a plaintiff need only demonstrate that an employer used a forbidden consideration with respect to an employment practice.

The statute does not mention, much less require, that a plaintiff show discrimination through direct evidence, the court said.

Moreover, the court added, Congress passed another Civil Rights Act in 1991 and could have required direct evidence in that statute. However, the court noted, it did not do so.

The court said that circumstantial evidence may, in some cases, be more certain, satisfying and persuasive than direct evidence.

Indeed, the court noted, it has never questioned the sufficiency of circumstantial evidence in criminal cases, even though proof beyond a reasonable doubt is required.