(Bloomberg) — The Republican plan to overhaul Affordable Care Act health coverage programs has a health problem.

On Wednesday, the U.S.’s biggest advocacy group for doctors came out against House Republicans’ legislation, adding to growing opposition from the country’s top trade groups for physicians and hospitals who worry that it will leave more people uninsured or with limited coverage.

Related: Hospital chains can’t move home-state Republicans on ACA

In a letter to Congress, the American Medical Association said Wednesday it “cannot support the AHCA as it is currently written,” referring to the American Health Care Act, as the Republican proposal to change major components of the ACA is named. The association calls itself the largest physician advocacy group in the country, and backed the nomination of Tom Price as President Donald Trump’s Health and Human Services secretary and point person on the ACA.

The association’s letter adds to growing objections to the bill, which would overhaul the current, income-based health premium tax credit subsidy and replace it with an age-based tax credit. In the last several days, other major physician groups, including the American College of Physicians, the American Academy of Family Physicians and the American Psychiatric Association, have said they have serious issues with or outright oppose the plan. Together they represent hundreds of thousands of U.S. doctors and health professionals.

Other industry trade groups have stayed largely neutral, including drugmakers and biotechnology companies. The health insurance lobby, America’s Health Insurance Plans, has yet to take a position on either side, though the group’s Chief Executive Officer Marilyn Tavenner said that “it’s important to us to keep as many members covered as possible.” 

Related: Tavenner asks Congress to save 2018 individual health market

Tavenner spoke at the group’s annual policy conference in Washington on Wednesday.

Tavenner was the head of the Centers for Medicare & Medicaid Services before she joined AHIP. At CMS, she helped run the major ACA coverage expansion programs.

A group for for-profit hospital companies opposes the current AHCA draft. (Photo: iStock)

Two hospital trade groups have problems with the current AHCA draft. (Photo: iStock)

Hospital opposition

The biggest hospital groups, the American Hospital Association and the Federation of American Hospitals, have also said they have serious concerns with the proposal

“We cannot support The American Health Care Act in its current form,” the American Hospital Association, which represents about 5,000 U.S. hospitals, said in a March 7 letter to Congress. The Federation of American Hospitals, which represents for-profit chains including HCA Holdings Inc. and Community Health Systems Inc., also said it had “significant issues” with the plan.

“We want to make sure that whatever comes out of this change really supports particularly those low-income Americans, who frankly don’t have the resources to afford coverage,” Chip Kahn, CEO of the hospital federation, said Wednesday at the health insurance forum in Washington.

Before Kahn took over as the head of the hospital federation, he was the CEO of the group that eventually became AHIP.

Related: HIAA president leaving to head hospital trade group

The AHCA legislation is going to be considered by two House committees today as Republican leaders attempt to quickly get it to the floor for a vote. Congressional actuaries have yet to issue a “score” that will show how much it will cost or save taxpayers, and how many people will lose or gain insurance.

Coverage changes

ACA coverage expansion programs pulled about 20 million people into public or private health insurance programs, bringing the U.S. uninsured rate to a record low. Under the Republican plan, about 2 million to 4 million people would lose coverage in the individual market starting in 2020, while another 4 million to 6 million would lose their Medicaid coverage, according to estimates S&P Global Ratings posted Tuesday.

The GOP plan has run into problems outside the health sector, as well. Conservatives have said they may not support it in Congress, which could imperil its passage in the House, or in the Senate, where Republicans have only a razor-thin majority. It’s also been panned by health experts who say it will reduce insurance coverage and provide weak coverage.

Trump ran on a promise to repeal the 2010 health law known as Obamacare, which he has said reduces employment and hasn’t worked to better health care, citing rising premiums and markets that health insurers have pulled back from.

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