Meanwhile, enrollment in HMOs fell to just 16 percent, the lowest level of enrollment seen since Mercer started its National Survey of Employer-Sponsored Health Plans in 1993. Enrollment in traditional PPOs fell as well, from 64 percent to 61 percent.

Read: CDHPs only plan that grew last year

According to Mercer, "many employers that did not already cover all employees working 30 or more hours said they would add a lower-cost plan for newly eligible workers, and this may have helped fuel CDHP growth in 2014. The average cost of coverage in a CDHP paired with a tax-advantaged health savings account is 18 percent less than coverage in a PPO and 20 percent less than in an HMO: $8,789 per employee, compared to $10,664 for PPOs and $11,052 for HMOs."

CDHP growth may also be spurred as employers look for ways to avoid paying the Cadillac tax in 2018. Mercer estimates that about a third of employers are currently at risk for triggering the tax in 2018 if they make no changes to their most costly plan.

"While new plan implementations are driving up CDHP enrollment, we are also seeing growth in enrollment in existing plans as employees become more comfortable with consumerism and employers provide them with tools to help manage the higher deductible," said Beth Umland, Mercer's research director.

Though CDHP are becoming more and more prevalent, employers are still continuing to offer traditional health plans along with CDHPs. Just 7 percent of all large employers, and 11 percent of jumbo employers, offered a CDHP as the only plan available to employees at their largest worksite in 2014, Mercer found. 

"While this practice may become more common — 18 percent of large employers say it's likely they will offer a CDHP as a full replacement within the next three years — for now it remains the exception," Mercer said.

Mercer collected data from 2,569 employers.