Independent directors of Askul Corp. criticized the company's biggest shareholder, Yahoo Japan Corp., for voting against their reappointment, escalating the public dispute before key meetings this week.

The negative vote "trampled upon" corporate governance at Askul and makes it "almost impossible for independent directors to oversee conflicts of interest," Kazuo Toda, Hideaki Miyata and Atsushi Saito told the Tokyo Stock Exchange in a statement on Sunday.

The rare instance of public bickering in corporate Japan first flared this month after Askul accused Yahoo Japan of violating the spirit of their agreement by demanding the sale of internet mail-order business Lohaco, which the two companies had jointly created in 2012. Yahoo Japan in turn wants to oust Askul's chief executive officer, Shoichiro Iwata, and the independent directors, saying it is unhappy with the firm's deteriorating business.

Without the backing of Yahoo Japan, Iwata risks losing his position at a shareholder meeting due Friday. Askul now plans to exercise its right to demand Yahoo Japan sell its 45 percent stake at a board meeting set for Thursday.

Whether it can force a sale hinges on the interpretation of an agreement struck when Yahoo Japan, which is backed by SoftBank Group Corp., first invested in Askul. Yahoo Japan has said it has no intention of off-loading the stake, worth about ¥67 billion.