Japan Inc. has made great strides in corporate governance over the past decade that buoyed the stock market and ignited interest in dealmaking. It is now facing a landmark test of those efforts in a case involving the Toyota group.

Minority investors are upset about the group¡¯s bid to take one of its listed affiliates private. They¡¯re concerned about a slew of issues, mainly pricing and a lack of disclosure. The outcome of the ?4.7 trillion ($31 billion) deal is being closely watched at home and abroad, especially in neighboring South Korea, which is starting to improve its own governance.

A letter signed by two dozen investors addressed ¡°widespread concern¡± about the plan to buy out Toyota Industries Corp., also known as TICO, the original company from which Toyota Motor eventually emerged. The world¡¯s biggest carmaker indicated last week there were no plans to raise the offer, which has been widely criticized for being too low, according to Bloomberg News.