Through years of acrimony over Affordable Care Act coverage for the poor and other individuals lacking health policies, one kind of insurance has remained steady, widespread and relatively affordable.

Employer-sponsored medical plans still cover more Americans than any other type, typically with greater benefits and lower out-of-pocket expense. Recent cost increases for job-based coverage have been a tiny fraction of those for ACA plans for individuals.

Now, as President Donald Trump promises a replacement for the Affordable Care Act that will provide "insurance for everybody," employers worry Republican attempts to redo other parts of the insurance market could harm their much larger one.

"We're deeply embedded" in the health law, said Neil Trautwein, vice president of health care policy for the National Retail Federation, a trade group. "Pick your analogy — it's like being tied to the railroad tracks … It's tough to disarm these things."

Business dislikes many parts of the ACA, including its substantial paperwork, the mandate to offer coverage and the "Cadillac tax" on high-benefit plans that takes effect in 2020. But large companies in particular — those that have always offered job-based insurance — say a poorly thought-out replacement might turn out to be worse for them and their workers.

"Whatever the Republicans are going to do, they've got to make it look as different from the ACA as they can" for political reasons, said Edward Fensholt, a senior benefits lawyer at Lockton Companies, a large broker. "There are some pieces that aren't broken, and the more you … make something different from the ACA, the more you risk screwing up things that look OK."

Any new health law needs substantial revenue to replace the Cadillac tax as well as ACA taxes on health insurers, medical devices and high-income households that paid for care expansion — assuming those measures are repealed. Otherwise, it risks stranding the millions getting government-subsidized ACA coverage.

One tempting solution for Republicans, big business worries, is to limit the exemption from income and payroll taxes that job-based coverage has enjoyed for decades. Taxing workers and employers for health benefits could raise billions to pay for a replacement plan.

Such a measure has occasionally been floated by Republicans since the days of President Ronald Reagan, often under the argument of leveling the field between employer plans and other coverage that the tax code treats far less generously.

Republicans are far from consensus on what a replacement should look like.

But capping the tax exclusion for employer plans is in replacement legislation introduced by Rep. Tom Price, the Georgia Republican poised to become secretary of Health and Human Services.

Depending on how it's structured, limiting the employer-plan loophole could add hundreds of dollars to workers' tax bills as a portion of their expensive health insurance is counted as taxable income.

The argument is a self-interested one for big business. A tax on health benefits would be a pay cut for its workers. Corporate payroll taxes would also rise if the value of worker health benefits counted toward required employer contributions to Social Security and Medicare.