One of Toshiba's biggest shareholders is opposing a plan to split the company into three separate businesses.
3D Investment Partners sent open letter to the Toshiba board on Wednesday, outlining its arguments.
The asset-management company claims that the process behind the plan lacked transparency and the proposal has failed to win over shareholders.
Singapore-based 3D Investment holds a roughly 7-percent stake in the Japanese conglomerate. It is the first major shareholder to express a view on the spin-off proposal.
Toshiba is planning to hold an ad-hoc shareholders' meeting by the end of March to hear investors' opinions.
Analysts expect that the letter may affect the opinions of other shareholders.