The commission, by contrast, said that under that law, it could establish “such reasonable exemptions” as it might find “necessary and proper in the public interest.” The United States Court of Appeals for the Third Circuit, in Philadelphia, upheld this claim in June, in the case filed by AARP, which has asked the Supreme Court to review the decision.

In its ruling, the appeals court said, “We recognize with some dismay that the proposed exemption may allow employers to reduce health benefits to retirees over the age of 65 while maintaining greater benefits for younger retirees.” But the court said the commission had shown that the exemption was “a reasonable, necessary and proper exercise” of its authority.

Under the new rule, employers may, if they choose, provide retiree health benefits “only to those retirees who are not yet eligible for Medicare.” Likewise, the rule says, retiree health benefits can be “altered, reduced or eliminated” when a retiree becomes eligible for Medicare.

Further, employers will be able to reduce or eliminate health benefits provided to the spouse or dependents of a retired worker 65 or over, regardless of whether benefits for the retiree are changed.

Employers and some unions contend that retirees under 65 have a greater need for employer-sponsored health benefits because they are generally not Medicare-eligible. Large employers have often provided some health benefits to retirees 65 and older, to help cover costs not paid by Medicare. But employers have for years been trying to reduce retiree benefits or to shift more of the cost to retirees.

Lawyers for the commission said the new Medicare drug benefit, now nearing the end of its second year, had strengthened the case for the regulation because it guaranteed that retirees 65 and older would have access to drug coverage. Younger retirees have no such guarantee, so employers may want to provide drug coverage to them in particular, the lawyers said.

Helen Darling, president of the National Business Group on Health, which represents large employers, welcomed the rule.