The other investor who owns 30% is not asking for this. I own 50% equity. I have been taking care of the day to day runnings of the business as CEO and Founder.
You may want to produce balance sheets and/or monthly a/c balances instead of giving access to all transactions & books. He is an investor and would be naturally keen to understand how his money is doing; however, as the owner and 50% equity holder, you may want to reserve the right to accessing all transactions.