Finance Committee Chairman Orrin Hatch, R-Utah, the Senate's chief tax writer, said Wednesday that the fines on people who go without coverage amount to a tax on working people.

WASHINGTON — Millions may forgo coverage if Congress repeals the unpopular requirement that Americans get health insurance, gambling that they won’t get sick and boosting premiums for others.

The drive by Senate Republicans to undo the coverage requirement under former President Barack Obama’s health care law is a sharp break from the idea that everyone should contribute to health care.

And just as important, it fits neatly with the effort by President Donald Trump’s administration to write new regulations allowing for skimpier plans with limited benefits and lower premiums.

Put the two together and the marketplace for about 18 million people buying their own health insurance could look very different in a few years. Consumers would have new options with different pluses and minuses. They’d notice a shift away from health plans that cover a broad set of benefits. New winners and losers would emerge.

Defending the GOP’s move, the Senate’s chief tax writer said Wednesday that the fines on people who go without coverage amount to a tax on working people. “It’s a terribly regressive tax that imposes harsh burdens on low- and middle-income taxpayers,” said Senate Finance Committee Chairman Orrin Hatch, R-Utah.

But Sen. Patty Murray of Washington, the ranking Democrat on the Health, Education, Labor and Pensions Committee, said repealing the requirement will undermine insurance markets and raise costs, particularly for those who need care. She accused Republicans of “sneaking devastating health care changes into a partisan bill at the last minute.”

The Congressional Budget Office has estimated that repeal of the insurance requirement would save the government $338 billion through 2027, mainly because fewer people would seek subsidized coverage. That would give GOP lawmakers money to offset some of the tax cuts they’re proposing.

CBO estimates the number of uninsured would rise by 13 million in 2027. Because fewer people would be paying into the insurance pool, premiums for individual plans would rise about 10 percent. Little impact was expected on employer coverage.

Repealing the mandate would be like taking away the stick that nudges people to get comprehensive health insurance, while the skimpier plans envisioned by the Trump administration’s regulation writers would be like new carrots introduced into the marketplace, said Katherine Hempstead, who directs health insurance work for the nonpartisan Robert Wood Johnson Foundation.

The result would be higher premiums for people who need comprehensive health insurance.