(Bloomberg) -- While Republican presidential candidates debatethe best way to repeal and replace Obamacare, Democrats have adifferent issue to work out: what to do about the law’s excise taxon high-cost employer-based health care plans.

On Tuesday, Hillary Clinton called on Congress torepeal the so-called "Cadillac tax" soon.“Too many Americansare struggling to meet the cost of rising deductibles anddrug prices,” Clinton said in astatement released Tuesday.

“That’s why, among other steps, I encourage Congress to repealthe so- called Cadillac tax, which applies to some employer-basedhealth plans, and to fully pay for the cost of repeal.”

Clinton weighed in after saying last month she wasworried the tax “may create an incentive to substantially lower thevalue of the benefits package” and shift costs toconsumers.

The announcement puts Clinton on the same side of the issue asSenator Bernie Sanders, who co-sponsored a bill that wouldrepeal the tax and issue a sense of the Senate that therevenue loss should be funded.

Sanders has opposed the tax since 2009, when heproposed an amendment to the Affordable Care Act to remove it fromthe bill. (Former Maryland Governor Martin O’Malley toldan AFL-CIO convention in Nevada last month that he alsosupports repealing the tax.)

Opposing the tax means that the three Democratic candidatesare now at odds with President Obama regarding one aspect ofhis health care law.

Clinton notes in her statement that “we should be defendingand strengthening the Affordable Care Act, not scrappingit.” It also forced them to come up with a viable solution toreplace the $91 billion in revenue the tax is expected to raise forObamacare over the next decade.

Sanders has supported replacing the revenue with a surtax on thewealthiest Americans, an alternative House Democrats proposed in2009. In her statement Tuesday, Clinton merely says that her“proposed reforms to our health care system would more than coverthe cost of repealing the Cadillac Tax.”

But opposing the tax also helps candidates gain favorwith labor unions and, potentially, the voters whose high-costplans will become less generous as the start of the taxdraws nearer.

Starting in 2018, employer-based health insurance planswill face a 40 percent tax for costs over $10,200 for an individualand $27,500 for a family, with those caps pegged to inflation infuture years.

Supporters of the tax, including the Obama administration, arguethat it will also help lower health care spending. But opponents,including labor unions, say that it will hurt the middle andworking class families it was meant to protect. In fact, theeffects are already being felt.

“As employers look to 2018 they’re starting to make cuts now,”Shaun O’Brien, the assistant policy director for health care andretirement at the AFL-CIO said in an interview. “Our folks who arenegotiating health care benefits are really worried aboutthis.” For unions, who negotiate health care benefits for 4 or5 year periods, the tax is already an issue, O’Briensaid.

While unions support more comprehensive plans, proponents of thetax say that beneficiaries of high-cost health plans are shieldedfrom the high costs of health care thanks to the low deductiblesand premiums of their plans.

If employers offer less generous plans, which the tax encouragesthem to do, then employees will have to pay more out of pocket.

That would lead to less unnecessary health care spending byemployees, supporters say, and less health care spending would helpkeep costs down for everyone. As healtheconomist Austin Frakt wrote at The Incidental Economist in2010:

The expectation is that, at least to some extent, insurers willbe motivated to craft policies that avoid the tax, developinnovations to reduce health care costs, and drive harder bargainswith providers. This will also likely mean that more health carecosts are shifted from premiums to out-of-pocket expenses. Thatshould encourage lower utilization and/or lower prices too.

But, opponents argue the tax will affect too many health plansand question the idea that people should have to pay more out ofpocket.

“At the end of the day this tax is designed to cut the use ofhealth care,” O’Brien said, adding that one of the more“disturbing” aspects of the tax was the idea that people need tohave higher deductibles and pay more out of pocket costs. Insteadof preventing unnecessary treatments, “what you really end up doingis hurting people with chronic conditions."

The limits for individuals and families doesn’t account forlocation or the age of people on the plans. And, because the limitsare tied to inflation and not the rate at which health costs rise(which is faster), more plans will qualify for the tax insubsequent years. An August report from the Kaiser FamilyFoundation estimated that, if insurance premiums rose at 5 percenta year, 26 percent of employers would offer at least one high-costplan. That number would rise to 42 percent by 2028. The nextpresident will be out of office before 2028, the presidentialcandidates who want to win over unions will have to come up withsolutions soon.

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