Who dislikes it?

A lot of people who are not economists. If it ever went into effect, the tax would either increase businesses’ tax burden or encourage them to offer their workers skimpier insurance. Neither outcome is much of a crowd pleaser.

It was Democrats who passed the Affordable Care Act, but in the years since many of the party’s leaders have denounced the Cadillac provision. In their 2016 presidential campaigns, both Hillary Clinton and Bernie Sanders said they wanted to repeal it. Republicans have a more mixed record on the tax. They tend to be more likely to favor proposals that would tax health benefits like income, but many don’t like the particular design of this tax — or the fact that it was part of Obamacare.

“It’s not popular in any way at all, and it’s not showed any signs of becoming any more popular,” said David Cutler, a Harvard economist who helped advise the Obama administration on health policy. “It’s very hard to find anyone who really wants it.”

Unions, in particular, have long loathed the Cadillac tax. Many of them have negotiated hard to preserve generous health benefits for their workers, often at the expense of salary increases.

If it’s so unpopular, how did it ever get passed?

The Cadillac tax is a good example of a public policy that probably never would have passed on its own. But it did not pass alone — it passed as part of a large package of health overhauls in the Affordable Care Act.

The Democratic leadership in Congress and the Obama White House wanted to be sure that the health bill would not increase the federal deficit, even though they also wanted it to expand government-subsidized health coverage to millions of low-income, uninsured Americans. That meant that the law’s writers were looking for ways to trim money out of the existing system in order to pay for the new programs.

The Cadillac tax was appealing because it was estimated to reduce health spending and raise revenue — and the economists close to Democratic politicians liked it. President Obama was also interested in ideas that would reduce the growth in health care spending, and he was persuaded that this policy could help do that.