The billionaire investor Dan Loeb has increased pressure on Sony's board by lifting his stake in the electronics group to 7 per cent.
The head of the $13bn (£8bn) hedge fund Third Point believes Sony should spin off its entertainment unit, which includes one of Hollywood's leading studios.
In a letter to its chief executive Kazuo Hirai ahead of its annual meeting tomorrow, Third Point said: "Sony appears to be regaining its competitive edge. Given our large stake, we reiterate our offer to serve on Sony's board of directors.
"It seems difficult to argue that entertainment would not be strengthened by the transparency that comes with public reporting."
Mr Loeb, one of the hedge fund industry's leading lights, is known for his aggressive investment style, which has rocked some of the largest companies in the world. In February, he dumped a $375m stake in Apple after revealing the technology group was in his top five losing positions in the fourth quarter of 2012.
A Sony spokesman said it was considering the proposal. The company has hired Morgan Stanley and Citigroup to look at options on Sony Entertainment – although experts said an IPO is not a foregone conclusion.