The justices, ranging in age from 53 to 87, are the last people to worry about such things in their own lives. They have life tenure and no mandatory retirement age.

Yet the justices are confronted by allegations of age discrimination in five cases this term. While the sheer number of cases probably can be explained away as coincidence, the topic is one of growing importance as more people work longer because of economic necessity or by choice.

"The importance of protecting older workers as the work force ages is enormous," said Stu Cohen, AARP's director of legal advocacy. "More older workers remain in the workforce and projections are that the percentage will continue to expand."

The percentage of people 65 and over who continue to work has grown from 10.8 percent in 1985 to 16 percent last year, AARP said. For people 55 to 64, the numbers also are up, from 54.2 percent in 1985 to 63.8 percent in 2007.

The Age Discrimination in Employment Act applies to workers who are at least 40. It prohibits discrimination based on age in hiring and firing, promotions and pay.

"Literally every employee at some point is going to be protected by it because all of us get older. It's true whether you are a male, female, minority or not. It's not true for any other statute. It's a very broad class of protected people," said Steven R. Wall, a partner at the Morgan, Lewis & Bockius law firm in Philadelphia.

The cases at the court this year include what kind of evidence an employee may present to bolster an age discrimination claim; whether retirement-age workers are entitled to disability payments; and whether federal workers who complain about age discrimination are protected from retaliation.

The last issue is the subject of oral arguments Tuesday in a case involving a postal worker in Puerto Rico who complained of both discrimination and retaliation. Federal courts dismissed the retaliation claim, saying there is nothing in the age discrimination law that allows such claims by federal employees.

Other anti-discrimination laws do provide protection from retaliation for government workers, said Eric Dreiband, former general counsel to the Equal Employment Opportunity Commission. The language in the laws are different "and it would appear deliberately different," Dreiband said.

The AARP and the National Treasury Employees Union are backing the employee.

The most important case from employers' perspective involves "me-too" evidence in a lawsuit filed by a woman who was 51 when she was laid off by a subsidiary of Sprint Nextel Corp.

The fight at the Supreme Court is over whether she should be able to introduce testimony from other employees who also say they were victims of age discrimination, even though they worked for other supervisors.

The employee, Ellen Mendelsohn, argued that such evidence is critical to establishing a culture of discrimination.

"Is it fair to an employer that somebody can call co-workers to testify, even though they had nothing to do with the plaintiff or her boss?" said Wall. "To sum it up from a management attorney's perspective, it's a very dangerous case because you can see how that applies no matter the form of discrimination."

A third case tests whether a retirement plan can treat disabled employees of different ages but similar tenures differently.

Kentucky's public retirement system prohibits employees who become disabled and are eligible for retirement from collecting disability retirement benefits, which can be more generous than regular pensions. The state says those employees are entitled only to their regular pensions.

By contrast, an employee who becomes disabled before he is eligible for retirement will receive a disability pension.

A former employee, backed by the EEOC, says the older worker often will receive lower benefits, sometimes dramatically so, in violation of the age discrimination law.

Decisions in all the cases are expected by late June.

As baby boomers get older, an increase in age discrimination suits seems likely, said David B. Ritter, a partner at the Neal Gerber & Eisenberg law firm in Chicago.

"Telling these folks they're too old or having them thinking that their younger boss thinks they're too old, they're not going to go quietly into the night," Ritter said.

Cohen, the AARP executive, said his group's research suggests that some people wish to continue working because they believe it will help them stay healthy.

Some workers also cling to their jobs because they need the health insurance, if not the paycheck. "They are mostly there out of necessity," Cohen said.