Story highlights Major interest groups have come out against the House GOP health care bill

They say it rolls back health care options established by Obamacare

Washington (CNN) The nation's leading hospital and doctor groups are lining up against the Republican health care bill, saying they fear millions of Americans will lose coverage.

The influential industry organizations, which helped the Affordable Care Act pass in 2010, are particularly worried about the bill's potential impact on lower-income and vulnerable Americans. These folks have been helped by the law's expansion of Medicaid and its subsides that are more generous for those lower on the income ladder.

The GOP bill would eliminate the funding for Medicaid expansion and curtail federal support for the entire Medicaid program. Also, it would replace the Obamacare subsidies with refundable tax credits that would likely provide less assistance for lower-income policyholders who buy their own coverage.

"It appears that the effort to restructure the Medicaid program will have the effect of making significant reductions in a program that provides services to our most vulnerable populations, and already pays providers significantly less than the cost of providing care," wrote Richard J. Pollack, CEO of the American Hospital Association.

The association voiced concern about the lack of Congressional Budget Office score that would estimate the bill's impact on coverage levels.

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