In a statement released this week, the head of the accounting firm admitted to "fear of one of the large accounting firms failing" and said "audit concentration, along with uncontrolled litigation exposure, is undermining the U.S. economic business model that served so well for so many years."

Nusbaum's request for a study on the matter came on the heels of a similar study in the United Kingdom, released this week.

The U.K. study, "Financial Reporting Council's Market Participants' Group," evaluated the country's audit market. The final report from the Council, according to U.K.-based AccountancyAge.com, recommends that all audit firms disclose the financial results of their statutory audits in order to improve competition and choice in the U.K. audit market. The report outlines 15 specific recommendations.

"Independence rules and conflicts of interest can also make it hard for the largest companies to switch between just a half-dozen firms," said Nusbaum. "Yesterday's U.K. report recognizes that the current status quo does not adequately address these issues and is not one to build the future on."

Nusbaum said, "We need a similar U.S. auditor concentration study with accompanying action steps to address the issue."

When Big Four accounting firms began to shed clients in 2002, when the Sarbanes-Oxley Act took effect, Grant Thornton was among the firms to gain clients. In 2004 alone, Grant Thornton said it picked up as many as 1,000 clients from Big Four firms.

Updated 04/26/07 to remove reference indicating GT is a Big Four firm.