The Big Four -- PricewaterhouseCoopers, Ernst & Young, Deloitte & Touche and KPMG -- once "had a lock" on the auditing business of companies with $1 billion or more in revenue, BusinessWeek reported.

Grant Thornton, the fifth-largest accounting firm, followed by BDO Seidman, McGladrey & Pullen, and the Crowe Group are gaining more business from the largest firms, because some businesses like the added attention they get. Others are seeking a smaller invoice because the time charged for audits has gotten larger.

The Sarbanes-Oxley Act, passed following several accounting scandals in the early 2000s, has increased the number of hours required for a typical audit by more than 30 percent, the New York Times reported.

Some Big Four firms have had to drop clients because of the added time needed to satisfy the Sarbanes-Oxley Act.