Toshiba Corp.'s biggest shareholder, Effissimo Capital Management Pte, called on the group's management Thursday to improve its "dysfunctional" governance, after an independent probe found the Japanese conglomerate had colluded with the government in influencing foreign activist investors.

In its first public statement since lawyers concluded earlier this month that Toshiba's general shareholders' meeting last year was not conducted fairly, Singapore-based activist fund Effissimo said it was alarmed that the very foundation on which a joint stock company rests had been compromised.

With this year's general shareholders' meeting coming up on June 25, Effissimo slammed the current Toshiba board as "ineffective," despite its decision to remove two outside directors from the list of nominees pending shareholder approval.