Many observers expect Congress to try to overturn a U.S. Supreme Court decision that may make it easier for employers to successfully defend age discrimination suits.

Observers point out that differences between the standard of evidence the high court in June established in this case for age discrimination cases vs. other discrimination lawsuits also could sow confusion among juries.

The Supreme Court held in its 5-4 decision in Jack Gross vs. FBL Financial Services Inc. that plaintiffs in age discrimination cases must prove age was the determinative factor in an adverse job action, not just one of several motivating factors, to successfully pursue their case.

Plaintiffs must prove their age “was the "but-for' cause of the challenged adverse employment action.” Otherwise, “the burden of persuasion does not shift to the employer to show that it would have taken the action regardless of age, even when a plaintiff has produced some evidence that age was one motivating factor in that decision,” said the court's majority opinion.

Congressional leaders are expected to seek legislation to overturn the decision, as they did in an earlier age discrimination case. In January, President Obama signed into law the Lilly Ledbetter Fair Pay Act of 2009, which eases time limits on age discrimination claims. The law reversed the Supreme Court's 2007 decision in Lilly Ledbetter vs. Goodyear Tire & Rubber Co. Inc.

In a statement shortly after the Gross ruling, Sen. Patrick Leahy, D-Vt., said he was troubled by the decision and pointed to the Ledbetter ruling.

Rep. George Miller, D-Calif., the chairman of the House Education and Labor Committee, said in July that he will hold a hearing to determine how the Gross decision will affect workers' protections against age discrimination and other forms of workplace discrimination. No date has been scheduled.

Meanwhile, observers say the decision could cause some jury confusion. They point out that in sex and other discrimination cases, plaintiffs have to establish only that discrimination was a motivating factor in an adverse employment decision, and it does not necessarily have to be the determinative factor.

Having two standards of evidence could confuse juries in cases, for instance, where a woman older than 50 accuses her employer of age as well as sex discrimination, experts say.