Identity thieves are everywhere, so if a mysterious caller asked for your name, Social Security number and address, red flags would go up. But here's a new twist: That caller might be a contractor for the Internal Revenue Service.

The federal agency is outsourcing collection of delinquent taxes—but at first you wouldn't know the IRS is behind a call because the debt collectors are instructed to say only that they are inquiring about "a personal business matter." Only after the individual verifies personal information is the reason for the call revealed.

Further, the private collectors are targeting low- and middle-income taxpayers—many of whom don't owe a dime.

Now Congress is getting involved. At a recent House Ways and Means Committee hearing, Rep. John Lewis, D-Ga., said the calls amount to "harassment, confusion and violations of taxpayer protections."

Many of the people contacted refused to disclose personal information, and the companies often continued to call them—repeatedly.

Kevin Brown, acting IRS commissioner, says the private companies have collected more than $19 million and insists that surveys show most taxpayers are satisfied with the collection agencies.

The companies sure aren't complaining. They get to keep 25 percent of everything they collect.