Most discrimination cases aren't so black and white, however, and the Mississippi case addresses one of the large gray areas. At issue are workplace policies that appear neutral but actually have a disproportionately harsh effect on older workers. Advocates for the aging say such subtle forms of bias reflect the real world, where few employers would be up front about intentionally favoring younger workers over older ones.
''Most employers are very astute. They're not going to throw out that smoking gun evidence that they are discriminating against the older people," said Laurie McCann, a lawyer for the senior citizens' group AARP.
Suits over what is called disparate impact can also involve instances when well-meaning policies of an employer, government, business, or other entity end up harming a minority or protected group. The Supreme Court already has said such lawsuits are allowed under the 1964 Civil Rights Act, which bans discrimination based on sex, religion or race.
The Age Discrimination in Employment Act, passed three years later, protects workers 40 and older by prohibiting age discrimination such as firing or refusing to promote an older worker, cutting pay solely because of age, or refusing to hire in the first place. The law does not expressly allow suits over the effect of policies that appear neutral.
The number of workers 40 and older averaged 74.5 million last year and the figure is now about 1 million more, the government estimates.
Overall, workers 40 or older are about half the nation's work force, and the number is growing. The federal government predicts that by 2010, 51 percent of workers will be 40 or older, a 33 percent increase since 1980.
In the Mississippi case, 30 officers and dispatchers sued over a pay plan that they said gave larger increases to employees under age 40. They lost in a lower court.
