Around one in 10 employers in the U.S. plans to drop health coverage for workers in the next few years as the bulk of the federal health-care law begins, and more indicated they may do so over time, according to a study to be released Tuesday by consulting company Deloitte.

The majority of Americans under age 65 who have health insurance get it through an employer. A big question about the law is whether companies will continue to offer coverage after a slate of changes starting in 2014 will give Americans more options for buying coverage without the help of an employer.

Most companies currently offer coverage voluntarily because they say it helps them recruit and retain workers. Critics of the overhaul argue that it could encourage companies to drop those plans if they become more expensive since the law requires them to provide a set level of benefits or pay a penalty.

Deloitte's findings differ from estimates by rival firm McKinsey & Co. last year that found 30% of employers say they would "definitely or probably" stop offering health insurance after 2014, as well as calculations by the Congressional Budget Office that estimated around 7% of workers could lose coverage under the law by 2019.

In all, 9% of companies in the Deloitte study said they expected to stop offering insurance in the next one to three years. Around 81% were planning to continue providing benefits, and 10% weren't sure.

But around one in three respondents said they could decide to stop offering health coverage if they find that the law requires them to provide more generous benefits than they do at the moment; if a tax on high-cost plans takes effect in 2018 as scheduled; or if they conclude that the cost of penalties for not providing insurance could be less expensive than paying for benefits.

Penalties for not providing health benefits after 2014 start at $2,000 per worker for companies with 50 or more full-time employees. Most companies already spend thousands of dollars more to cover each worker, although those costs come with tax breaks and can also reduce the wages that employees expect.

The study, conducted between February and April, surveyed corporate and human-resources executives from 560 companies currently offering benefits, Deloitte said. Companies weren't named in the report. The survey was done before the Supreme Court ruled to uphold the overhaul law in June. The firm said it doesn't believe that affects the results, as most employers didn't seem to expect the law would be voided.

Employers, especially large companies, have been reluctant to talk openly about their coverage plans for 2014. A few small firms have testified before Congress that they are thinking about dropping coverage.

Those differences were visible in the latest findings. Fewer than 2% of companies with more than 1,000 workers said they were considering dropping coverage. Companies with 50 to 100 workers were most likely to say they would drop coverage, with 13% of them saying they expected to do so in the next one to three years.

Only 16% of respondents said that they would be likely to stop offering health benefits if their competitors did.

A spokeswoman for the Department of Health and Human Services, Erin Shields Britt, said that the passage of a law in Massachusetts requiring employers to provide insurance or pay a penalty and creating new options for individuals to buy coverage had led to an increase in the number of people in that state who received health insurance at work.

"This law will decrease costs, strengthen our businesses and make it easier for employers to provide coverage to their workers," she said.

Benefits consultants have also said that their clients are considering changes to the way they offer coverage that fall short of dropping insurance altogether, including requiring employees to pay a greater share of costs, paying only a fixed amount toward workers' costs, and giving employees more generous insurance arrangements if they show healthy behaviors.

The Deloitte study found that many of those actions were already taking place. Around three quarters of respondents said they had increased the amount that employees contributed to their plans, and a similar proportion said they would do so in coming years.

Among the largest companies, around 70% said they had increased incentives for employees who exercised or enrolled in disease-management programs, and one in five said they had shifted to paying only a set amount toward insurance.