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 health law.

The association’s letter adds to growing objections to the bill, which would eliminate much of Obamacare and replace it with smaller tax subsidies to buy insurance.

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 said they have serious issues with or outright oppose the plan. Together they represent hundreds of thousands of U.S. doctors and health professionals.

Related: Hospitals, advocates raise alarms about ACA repeal

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

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.

The 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

Obamacare provided insurance to about 20 million people, 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 an estimate from S&P Global Ratings 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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