NEW YORK (CNN/Money) - CMS Energy became the latest company to part ways with troubled accounting firm Arthur Andersen LLP, the energy trader said Tuesday as it disclosed plans to form a special committee to investigate swap trades.

Shares of CMS Energy (CMS: down $0.99 to $15.80, Research, Estimates) fell more than 7 percent in trading Tuesday after the announcement.

CMS, which said last month that it planned to restate financial results for 2000 and 2001 due to questionable trades that inflated revenue by billions, said Tuesday that Andersen decided not to audit the firm's restated results. CMS has hired Ernst & Young to audit its restated financial statements once the special committee's investigation is complete.

Andersen was indicted earlier this year on obstruction of justice charges for its alleged role in shredding documents related to fuzzy accounting at another energy trading client, Enron Corp., which filed for bankruptcy shortly after investors learned of the irregularities. Andersen is awaiting a verdict in the just-completed criminal trial regarding the charges.

More than 600 of Andersen's 2,300 clients have left the company since the indictment.

CMS Energy said Tuesday that Andersen dropped it because it can no longer rely on historical opinions for the periods being restated. However, Andersen notified CMS that its decision does not apply to separate audited statements for the Consumers Energy and Panhandle Eastern Pipe Line Company for the same period.

Andersen officials could not immediately be reached for comment on the matter Tuesday.

The special committee being formed by CMS will investigate so-called "round-trip" trades designed to artificially boost a company's trading volume and revenue.