Consider, for example, a company that refuses to hire people who've been unemployed for six months or more. Older workers who lose a job are much more likely to remain unemployed for that length of time than younger workers, according to Laurie McCann, an attorney for AARP Foundation Litigation. That policy could well have a disproportionate impact on older workers, and a company with such a policy could now come under EEOC scrutiny.

In such cases, employers would be required to show that they based their business decisions on reasonable factors other than age. The new rule provides clear guidance about what is considered reasonable, whereas before, McCann says, just about "everything was deemed reasonable." 

"As a result of this new rule, employers should be more careful when they conduct a reduction in force, formulate a hiring policy or formulate a policy as to who gets a promotion," McCann says. "If it would harm older workers, they'll hopefully look to see if there's another way to make business decisions without this adverse impact. This will improve workplace conditions for older workers."

AARP Executive Vice President Nancy LeaMond says that for workers, the practical outcome of the new guidelines is that there will be a better chance of preventing discrimination before it happens. In the event it does occur, older workers will have a chance to get their day in court and prove their cases.

The EEOC proposed the rule in 2010 to clarify a 2008 U. S. Supreme Court decision (Meacham v. Knolls Atomic Power Laboratory) that held that policies or practices with an adverse impact on older workers were in violation of the Age Discrimination in Employment Act of 1967 unless they could be justified by a reasonable factor other than age.

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Carole Fleck is a senior editor at AARP.org.