Is there a particular reason that you would want more than one account?
If it's because you have multiple websites and/or blogs you can just use the same account. The wording on Amazon says this: "You don't have to have multiple Associates accounts". It says you don't have to have multiple accounts, it doesn't say you can't have multiple accounts.
I wasn't able to find any reliable information on the web for this so I would recommend getting in touch with Amazon and get a straight answer directly from them. You don't want to take a chance and loose the account you have and the money in that account because they are known to not pay out for violations of their terms.