The American Medical Association, a powerful lobbying group representing the nation’s doctors, announced on Wednesday that it opposed the House Republicans’ proposed legislation to replace the federal health care law, saying it was concerned the bill “would result in millions of Americans losing coverage and benefits.”

The group, which provided crucial support for the Obama administration’s contentious health care legislation before it was enacted in 2010, also sent a letter to the two House committees responsible for drafting the Republicans’ bill, called the American Health Care Act. The group’s concerns echoed some others raised this week among industry organizations like hospital groups worried about the possible losses of coverage that could result from the proposed legislation that was released on Monday.

All of the major hospital groups, including the American Hospital Association, also came out against the bill. “We are very concerned that the draft legislative proposal being considered by the House committees could lead to tremendous instability for those seeking affordable coverage,” the hospitals said in a letter to Congress. The hospitals also raised concerns about Republicans’ plans to significantly alter Medicaid, which they said could result in a loss of coverage and cuts to health care services.