A new report is challenging the fairness of Internal Revenue Service criminal prosecutions, spotlighting cases where small U.S. cities had more convictions per capita than major business centers.

The Senate Finance Committee, which is preparing another series of high-profile hearings looking into IRS horror stories, is expected to review the report just two weeks after the April 15 tax-filing deadline.The committee also is expected to hear cases alleging IRS agents abused citizens' rights in criminal tax cases, according to several sources who have met with Senate investigators.

The study by the Transactional Records Access Clearinghouse, or TRAC, reported per capita tax convictions were twice the national average in IRS offices in Pensacola, Fla.; Greensboro, N.C.; Memphis, Tenn.; and Charleston, W.Va.

But major business centers, including Los Angeles, Chicago, Boston and Detroit, reported lower than average criminal convictions, TRAC said.

The IRS said the TRAC data and the study's conclusions are flawed. But David Burnham, an author and research professor with Syracuse University who helped prepare the study, said the variation raises troubling questions about management of IRS criminal matters.

"You can see large and hard-to-explain variations on the criminal side that I think raise questions about fairness and effectiveness of the agency," Burnham said.

A senior IRS official criticized the TRAC report.

"We think there are a number of issues there that make that data incorrect," said Ted F. Brown, IRS assistant commissioner for criminal investigations. Brown said problems with the TRAC data result in "conclusions that are misleading."