A new report says the number of large companies being audited by the IRS has fallen in the past 20 years, but this comes as more small and mid-sized businesses are coming under scrutiny.

The Transactional Records Clearinghouse says there's been "historic collapse" in audits for corporations holding at least 250-million dollars in assets.

The IRS isn't disputing the data, but says it disagrees with suggestions that it's easing oversight of the biggest corporations.

The agency says it's focusing resources on areas of non-compliance, inspecting tax shelters, "extraordinarily complicated" partnerships and those corporations where shareholders -- not the company -- have to report income or losses.