Dan Loeb's activist hedge fund, Third Point, called Sony's entertainment division "poorly managed" and compared its would-be summer blockbusters "After Earth" and "White House Down" to the costly box-office embarrassments "Waterworld" and "Ishtar."
"[Sony] Entertainment remains poorly managed, with a famously bloated corporate structure, generous perk packages, high salaries for underperforming senior executives, and marketing budgets that do not seem to be in line with any sense of return on capital invested," the letter said, after a lengthy section praising the positioning and management of Sony's electronics division.
The letter called out Sony CEO Kazuo Hirai for his statement a few weeks ago about the box-office losers. "I don't worry about the entertainment business—it's doing just fine."
"We find it perplexing that Mr. Hirai does not worry about a division that has just released 2013's versions of 'Waterworld' and 'Ishtar' back-to-back," the letter said. Instead, it said, the company gave a pass to Sony Pictures Entertainment co-CEOs Michael Lynton and Amy Pascal, the executives responsible "for these debacles."
(Read more: Sony suffers second box-office letdown as it eyes partial spinoff)
The letter went on to express "surprise that Sony's CEO does not worry that Entertainment continues to generate profitability levels far below those of its competitors."
Sony has been considering spinning off as much as 20 percent of the studio at Loeb's urging. Third Point owns 6.9 percent of the company.
—By CNBC's Matt Twomey. Follow him on Twitter @Matt_Twomey