The nation's regional banks need a little shaking up: There are far too many of them, profits from loans are shrinking, and their customers are disappearing. The enormous privatization of Japan Post, coming up next month, may just help spur them into action.

State-owned Japan Post Bank Co., one of three companies going public as part of a $12 billion initial public offering in November, currently has restrictions on its business that could eventually be loosened once it is public, allowing it to make loans and accept higher amounts of deposits than currently permitted.

That will put the biggest collector of Japanese savings into more direct competition with the country's more than 100 regional banks, which are resisting calls to merge even as their prospects dim.