"Any cut or restructuring of Medicaid … is simply a cost shift to states and families," the groups wrote. "As our economy struggles to recover, now is not the time for the federal government to shift costs to states and families."
Liberal advocacy group Families USA distributed the letter to reporters.
"Budget debates are always about priorities, and it would be difficult to find a program more vital than Medicaid in terms of its importance to America’s families," said Families USA Executive Director Ron Pollack in a statement.
"There’s no ‘fat’ in this program to cut. Cuts to Medicaid mean cuts to actual delivery of healthcare. Cuts to Medicaid mean more financial hardship for struggling families and more financial hardship for burdened state budgets."
Pollack added that the organizations that co-signed the letter represent "many millions of Americans."
The groups ranged from the American Academy of Pediatrics to the NAACP to the National Coalition for LGBT Health.
President Obama and congressional Republicans are still negotiating over how to avoid the combination of tax hikes and spending cuts set to take effect in January.