Ryan said some firms are also doing "dependent audits"—checking to see if a worker's child or other claimed dependent is actually eligible for the health plan—which can further reduce costs.
In other findings, ADP's survey shows that the rate of young adults who get health coverage through their job at larger companies has significantly fallen under Obamacare.
Adults under age 26 long have opted into job-based health plans at a lesser rather than older counterparts. Before Obamacare launched, that group had a so-called take rate in job-based plans at nearly 57 percent—which was 18 to 21 percentage points less than older workers, the ADP survey showed.
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But in the years since the ACA has been in effect, and allowed people under age 26 to remain on their parents' health plans, the take rate among that group fell by 12.6 percentage points to just 44.1 percent. At the same time, the take rate among all older groups "decreased only slightly," the report said.
The survey also found that while the percentage of full-time workers offered health insurance grew by 2 percent, the number of eligible employees who opted in dropped by nearly the same percentage, keeping overall participation steady at 69.3 percent of workers.
The report comes three months after another survey of large employers by ADP found that most such companies have or plan to extend health benefits to workers beyond the requirements of Obamacare, which only mandates such offers to employees who work 30 hours or more per week.
That earlier survey also found that a majority of large companies are not planning to modify workers' hours in an effort to get under that so-called employer mandate of Obamacare.