The American Hospital Association has already said no to House Republicans’ health care bill.

“We ask Congress to protect our patients, and find ways to maintain coverage for as many Americans as possible,” Richard Pollack, president of the association, wrote in a letter to House Republicans. “We look forward to continuing to work with the Congress and the Administration on [Affordable Care Act] reform, but we cannot support The American Health Care Act in its current form.”

The American Hospital Association — along with other members of the industry, like the American Medical Association — is widely credited with playing a key role in the passage of the Affordable Care Act (also known as the ACA or Obamacare). That the group is withholding its support suggests Republicans could face a well-organized and well-funded opposition within the health care industry to kill the bill or at least change its provisions.

The American Hospital Association cites two major problems: First, the legislation has not been scored by the Congressional Budget Office — so there’s no official estimate for how many people will lose (or gain) health insurance as a result of the bill. Second, the bill cuts back on programs, particularly the Medicaid expansion and tax credits for health insurance, that make health care affordable and accessible to millions of people.

All of that conflicts with the association’s stated goal to “maintain coverage for as many Americans as possible.” Indeed, a Standard & Poor’s analysis concluded that the bill will cost 6 million to 10 million people their health insurance, out of the 22 million who gained access to health coverage through Obamacare.

“We believe that any changes to the ACA must be guided by ensuring that we continue to provide health care coverage for the tens of millions of Americans who have benefitted from the law,” Pollack wrote. “We believe the legislation needs to be reviewed through this lens, and carefully evaluated regarding its impact on both individuals and the ability of hospitals and health systems which are the backbone of the nation's health care safety net in terms of our ability to care for all of those who walk through our doors.”

The association also argued against the bill maintaining Obamacare’s reductions in payments to hospitals. “If coverage is not maintained at the current level, those resources need to be returned to hospitals and health systems in order to provide services to what will likely be an increased number of uninsured Americans,” Pollack wrote.

The American Hospital Association is just the latest among several major groups to come out against the health care law. Senate Republicans seem very skeptical of the bill, and some have already come out against it. And major conservative groups, such as Heritage Action, have thrashed the bill as “Obamacare lite” and “Obamacare 2.0.”

The bill still has time to be amended before it’s voted on by the House and Senate. But the initial reception is far from an ideal start for one of the biggest pieces of legislation in the Republican agenda.

For more on House Republicans’ Obamacare repeal bill, read Vox’s explainer.