The logo of Toshiba is seen as a shareholder arrives at an extraordinary shareholders meeting in Chiba, Japan, March 30, 2017.
The letter, seen by Reuters, is from 3D Investment Partners, which owns a 7.2% stake in Toshiba.
It is likely to heighten scrutiny into governance at Toshiba, a renowned industrial conglomerate in crisis sparked by Thursday's report.
The company was holding an emergency meeting on Sunday to discuss reassigning the candidates for three key board committees ahead of a June 25 shareholder meeting.
Major shareholder advisory firms recommended against some of the candidates, including the four addressed in the 3D letter.
Toru Hanai, Toru Hanai Toshiba Corp's, Thursday's, Osamu Nagayama
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