We ask that you immediately make public the letter(s) in which Yahoo invited third parties to make proposals for the company, Loeb's New York-based Third Point Capital demanded.
Sunnyvale, Calif.-based Yahoo didn't issue an immediate response.
Loeb bought into the search engine and media company after CEO Carol Bartz, 63, was fired over Labor Day weekend. Subsequently, Yahoo retained Goldman Sachs and Allen & Co. for advice, including a potential sale or invitation to a private equity company to acquire a friendly stake.
Large private equity companies, including Silver Lake Holdings, KKR, Providence Equity Partners and TPG have been reported by investment bankers as having signed non-disclosure agreements to see Yahoo's financials.
Separately, Jack Ma, CEO of China's Alibaba Group, in which Yahoo owns a 44 percent stake, announced he'd like to acquire the entire company and was seeking financing from Singapore state investment company Temasek Holdings.
Loeb, who's previously shaken up other companies and sent two critical letters to Yahoo, claims the process isn't fair and continues mismanagement given the history of strategic bungling by Yahoo board chairman Roy Bostock and founder Jerry Yang.
Loeb said he doesn't need to know who's been given the financial data. He just wants to see it himself.
Yahoo shares have gained about eight percent since the Bartz ouster. The shares closed at $15.42, down a nickel Tuesday, giving the company a market capitalization of $19.13 billion.