Dara Smith, a lawyer representing AARP. The organization has filed a lawsuit against the Equal Employment Opportunity Commission over its rules for employee wellness programs. Credit Justin T. Gellerson for The New York Times
Employers have raced to offer workers a hefty financial incentive to sign up for programs meant to improve their health, submitting personal medical details in the process. But as these programs have spread, so has resistance — with employees dubious about sharing that information with employers.

On Monday, that tension erupted in a federal lawsuit against the government agency that handles the rules on these so-called wellness programs. It is the first major legal challenge of the rules, and will add fuel to one of the hottest debates in health care.

The suit, filed by AARP, the large consumer advocacy group that represents older Americans, argues that these programs violate anti-discrimination laws aimed at protecting workers’ medical information. It also questions whether the programs are truly voluntary, because the price of not participating is high for some workers.

The target of the suit is the Equal Employment Opportunity Commission, the federal agency responsible for issuing the rules governing what employers can do. The agency issued new rules on the programs in May.

The final rules issued by the commission allow an employer to set the incentive as high as 30 percent of the annual cost of a worker’s health insurance coverage. The rules sought to clarify uncertainty over how employers can plan wellness programs. They go into effect in 2017.

The AARP is seeking a preliminary injunction. The commission declined to comment on the suit, which was filed in Federal District Court in Washington.

Many employers have instituted wellness programs, which might include initiatives to help workers stop smoking or manage a chronic condition like diabetes. Under the Affordable Care Act, the law that overhauled the health care system, companies can use financial incentives as a carrot — or stick, depending on one’s vantage point — to entice more employees to participate in these programs. The goal is to reduce overall health costs.

At issue is whether some programs that require an employee to fill out a health risk assessment or undergo biometric testing for conditions like high blood pressure are forcing workers to hand over private medical or genetic information.

Critics, which have included the Equal Employment Opportunity Commission, say some programs violate anti-discrimination provisions under other laws like the Americans with Disabilities Act. Those provisions are meant to protect someone with depression or a genetic predisposition for breast cancer, for example, from having to tell an employer about a condition.

In issuing the final rules, the commission seemed to reverse course, said Dara Smith, a lawyer representing the AARP, in making sure that giving out private medical information remained strictly voluntary.

“Everyone expected that the E.E.O.C. would continue its old approach,” she said.

The agency has aggressively pursued cases in which it argues employers have overreached with wellness programs. Employers have typically favored more latitude in being able to persuade employees to sign up for wellness programs and provide medical information that will help them better manage any chronic conditions. The commission, on the other hand, has said that some of these efforts violate anti-discrimination laws.

The agency has had a mixed legal record, however. It also faced pressure from the White House and others to avoid derailing employers’ efforts, which were seen as central to containing health care costs.

Now, the AARP argues, the agency’s rules “enable employers to pressure employees to divulge their own confidential health information and the confidential genetic information of their spouses as part of an employee ‘wellness’ program.”

The cost of individual coverage averages $6,435 a year, according to the Kaiser Family Foundation, which means workers could be forced to pay nearly $2,000 for refusal to participate.

“On average, these penalties would double or even triple those employees’ individual health insurance costs,” the AARP contends in its lawsuit.

While the AARP says employers are welcome to offer wellness programs that ask for medical information, it says they should be truly voluntary.

“It would be very difficult to have an across-the-board number that wouldn’t coerce anybody that wasn’t zero,” Ms. Smith said.