The American Hospital Association on Monday urged Republican senators to make sure hospitals are reimbursed if the number of uninsured patients grows following the passage of a healthcare bill that would repeal and replace portions of Obamacare.

"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 the additional millions of Americans who will become uninsured," AHA wrote in a letter.

The group mainly voiced its objections to provisions in the House-passed bill, the American Health Care Act, asking the Senate not to pass it because it threatens to increase the rolls of uninsured. AHA said it opposed changes to Obamacare's insurance protections and worried about the impact that reductions in coverage would have on the opioid crisis.

Republicans in the Senate have been writing their own bill, and deep divisions have emerged on Medicaid, insurance protections and funding for Planned Parenthood.

The group said it did not oppose changing Obamacare's tax subsidies to buy private coverage into tax credits, but offered that they should be more generous for people who are older and have lower income. Senators already have said this is a priority for them.

AHA pointed to projections about the bill made by the Congressional Budget Office showing that the number of uninsured would grow by 23 million people by 2026 and that Medicaid spending would be reduced by $834 billion over the same period. It warned that "serious negative consequences for communities across America" would result from the House bill's changes to Medicaid that would turn federal payments to a fixed sum each year, whether though a per-capita cap or a block grant.

Obamacare was originally written to mandate all states expand Medicaid to low-income people, but a Supreme Court decision made the provision optional for states. Now, 31 states and the District of Columbia have expanded the program, which is mostly paid for by the federal government. Though Medicaid payments to hospitals are lower than those from private insurers, the expansion still has provided hospitals will less uncompensated care, and the group has urged that the Senate not only maintain expansion but allow other states that have not done so to follow.

Senate leaders are aiming to pass a bill ahead of the Fourth of July, though rank-and-file members have expressed doubt about the deadline.