The case was closely watched by business groups, who argued that allowing younger workers to file age discrimination claims would place many employee benefit plans in jeopardy.

Quentin Riegel, vice president for litigation with the Washington-based National Association of Manufacturers, said that employers would have been forced to revisit any number of benefit policies and likely would have begun to limit coverage for all employees in order to avoid a new type of liability.

In the case of General Dynamics v. Cline, an employee in his 40s challenged a collective bargaining agreement between his employer, General Dynamics, and the United Auto Workers which eliminated the company's obligation to provide retiree health benefits except for then-current workers who were at least 50 years old.

The employee, Dennis Cline, argued that since he was at least 40 years old and thus protected by ADEA, the agreement to eliminate his retiree health benefits illegally discriminated against him.

He filed a complaint with the Equal Employment Opportunity Commission, which agreed with him and which urged General Dynamics and the UAW to settle his claim.

When they could not reach an agreement, Mr. Cline filed a lawsuit.

A United States District Court dismissed the complaint, stating that no court had ever granted relief for reverse age discrimination under ADEA.

But the Sixth Circuit Court of Appeals reversed the lower court, reinstating the lawsuit.

Citing the clear language of ADEA, the Sixth Circuit said it is so clear on its face that the statute covers discrimination against any worker based on age, that if Congress had meant to limit its scope, it would have done so.

But in an opinion written by Justice David Souter, the Supreme Court reversed the Sixth Circuit and dismissed the action.

In its decision, the court said that if Congress had been worried about protecting the younger against the older, it would likely not have ignored everyone under age 40 by limiting the class of those protected by ADEA to individuals aged 40 and over.

The ADEA, the court said, is a remedy for unfair preference based on relative youth.

The court also refused to grant deference to the EEOC's view that ADEA does protect relatively younger workers. The EEOC's interpretation is clearly wrong, the court said, and so its view is not entitled to deference.