Health FSA fans will be in for a further rude surprise as their employers attempt to reduce the effect of the tax on their bottom line through other strategies, such as increasing deductible limits, cutting the number of health plans available to workers, offering narrower networks of doctors and hospitals, and eliminating covered services.
"One of the effects [of the tax] will likely be cutbacks in benefits," Levitt said. "The breadth of effects from this tax grow significantly over time, and eventually the vast majority of workers will find themselves with changes in their health benefits as [a result] of this tax."
Kaiser's analysis also highlights the fact that the Cadillac tax costs can be different for different employees within the same company, even if they are enrolled in the same health plan, further complicating companies' compliance with the law. Employees who use FSAs will be more apt to trigger the tax, and more apt to generate a higher tax amount, than employees who don't use FSAs.
While not all eligible workers use FSAs, those that do often find them useful for reducing the cost of their out-of-pocket medical expenses, given their use of pre-tax dollars.
A spokesman for the human resources consulting firm Aon Hewitt noted that "almost all large employers offer health-care FSAs," and that participation in them among employees ranges from 17 to 20 percent.
Benefits management giant ADP said that the average health FSA annual election in 2015 for the 1.5 million such accounts it manages was $1,300, up $100 from the average in 2013. A spokesman said that the uptick is likely the result of a rule change that allows participants to carry over up to $500 into the next year, as opposed to forfeiting that unused money.
In contrast, the Cadillac tax is a particularly unpopular, yet key element of the Affordable Care Act, and one that is drawing renewed calls for its demise.
"It's a tax that deficit hawks and economists love, but every other interest group hates," Levitt said.
The tax is designed to generate revenue—an estimated $87 billion over a decade—to help fund the federal government's expansion of health insurance coverage to more Americans through subsidies to customers of Obamacare plans sold on government exchanges, and through expanded Medicaid benefits.
The Cadillac tax is also designed to help decrease overall health-care spending inflation by imposing a steep levy on high-cost insurance plans, discouraging overuse of medical services. Most Americans, about 160 million people, are covered by job-based health insurance plans.
It is "one of the strongest cost-containing measures in the ACA," Levitt said.