In no event shall an industrial loan company have outstanding at any time its investment certificates (exclusive of those hypothecated with the company issuing them) in an aggregate sum in excess of 20 times the aggregate amount of its paid-up and unimpaired capital and such of its unimpaired surplus as is declared by a bylaw of the company to be not available for cash dividends. The commissioner by rule or by order issued pursuant to Section 18315, may limit the amount of outstanding investment certificates of an industrial loan company.