Debt-collectors for Accretive sometimes do not identify themselves, leading patients to believe they are hospital caregivers, the report stated.
And documents obtained by the Times reportedly show that Accretive employees sometimes "stall" patients entering emergency rooms until past debts are settled.
The suspicious practices were revealed by the Minnesota attorney general's office, which is investigating the debt-collection firm, the Times reported.
Asked to comment by the paper, an Accretive spokeswoman said in a statement, "We have a great track record of helping hospitals enhance their quality of care."
Stark, a ranking member of a Ways and Means subcommittee on health, wrote to the Center for Medicare and Medicaid Services (CMS) and the Department of Health and Human Services (HHS) demanding the group come under federal investigation.
"To the extent these activities violate federal law," he wrote to CMS administrator Marilyn Tavenner, "I request that you report back to me on federal enforcement measures that CMS can and will undertake."
Stark added that if the practices are illegal, hospitals that participate in Medicare should be warned of "possible enforcement action."
Shares of Accretive Health fell 42 percent Wednesday, according to reports.
Dem: Alleged medical debt shakedowns 'corporate greed at its worst'
By Elise Viebeck - 04/26/12 07:30 PM EDT