A 1989 Supreme Court ruling held that in order to win a mixed-motive case employees must provide direct evidence that discrimination had been a motivating factor in the employer's action. In 1991, the Civil Rights Act was amended, and no mention was made as to the need for direct evidence in proving discrimination. However, many lower courts continued to require direct evidence. The decision in the case of Desert Palace v. Costa changed this by holding that direct evidence was not necessary.
See "Justices Provide a Victory to One Category of Job-Bias Plaintiffs", Linda Greenhouse, The New York Times, June 9, 2003