The main lending unit of Japan's biggest bank may quit as one of the 22 primary dealers that underwrite government bond auctions, potentially becoming the first major financial firm to withdraw since the Bank of Japan introduced negative interest rates this year.

Bank of Tokyo-Mitsubishi UFJ Ltd. is considering the move and nothing has been decided, spokesman Kazunobu Takahara said Wednesday. A Finance Ministry spokesman was not immediately available for comment.

The lender would continue to participate in auctions and purchase Japanese government bonds as needed, people with knowledge of the matter said, asking not to be identified as the deliberations are confidential.