The lawsuit, pending in circuit court, accuses PricewaterhouseCoopers, KPMG LLP and Ernst & Young LLP of overbilling thousands of clients over a 10-year period dating back to 1991, the Wall Street Journal reported.

The closely held Warmack-Muskogee Limited Partnership filed the lawsuit in Texarkana, Ark., that alleges the accounting firms operated under an agreement not to disclose travel deals and rebates to clients or to credit clients for the rebates.

The plaintiff has requested the lawsuit be certified as a class action, which could expand the case to include most publicly held corporations in the United States, the Journal said.

The lawsuit alleges the rebates retained by the various firms were for up to 40 percent of the purchase price of travel services.

The defendants deny the allegations, but so far the lawsuit has cost PricewaterhouseCoopers an estimated $10 million to gather and analyze information pertaining to the suit.