WASHINGTON -- A congressional probe found that 27,000 doctors, hospitals, nursing homes and hospices paid by Medicare failed to pay more than $2 billion in federal taxes in 2006, and Medicare officials now say they are taking steps to stop the abuse.

The Government Accountability Office, Congress's investigative arm, reported that the total included $896 million in payroll taxes and $581 million in individual income taxes. Medicare, the federal insurance program for the elderly and disabled, is also the nation's largest health-insurance program.

The GAO said its own numbers are "substantially understated" because it didn't include all Medicare providers, among them those that didn't file tax returns.

The report, ordered by the Senate Homeland Security and Governmental Affairs Committee's investigations panel, is the result of the third tax-fraud probe involving health-care providers. Last year, the GAO found 21,000 of Medicare's doctors and outpatient services owed $1 billion in taxes through September 2005, and 30,000 providers of Medicaid services, the state-federal health-care program for the poor, owed more than $1 billion through September 2006.

Lawmakers have been pressing the Centers for Medicare and Medicaid Services to adopt the Federal Payment Levy Program that would allow the Internal Revenue Service to withhold government payments to contractors that owe taxes. Putting pressure on CMS, Investigations-Panel Chairman Sen. Carl Levin (D., Mich.) and Sen. Norm Coleman of Minnesota, the panel's ranking Republican, introduced legislation last year that would require Medicare to use the payment levy program for doctors, hospitals and outpatient services that provide services for Medicare patients.