Bill Ackman delivered the latest punch in one of the biggest fights on Wall Street, this time warning major accounting firm PricewaterhouseCoopers that it could face "substantial liabilities" for its work in certifying Herbalife's books.
The CEO of Pershing Square Capital Management—who has called Herbalife a "pyramid scheme" and placed a $1 billion short bet against it in December—sent a letter to PwC executives Aug. 29 , with copies to the Securities and Exchange Commission and three Herbalife directors who sit on its audit committee.
"If we are correct that Herbalife is a pyramid scheme and PwC fails to accurately inform investors of this risk, PwC may incur substantial liabilities in the event of the Company's failure," Ackman wrote in the letter, which was obtained by CNBC after it was sent to Pershing Square investors last night.
The hedge fund manager also asked PwC to review accounting issues that it claims to have found and that it detailed in the 52-page letter.
(Read more: Ackman's fund flat, sharply trailing S&P: Sources)