Remove "New Customer" registration

I need help removing or disabling the NEW CUSTOMER? login from the Customer Center login first page. 

Current customers that should be logging in under the RETURNING CUSTOMERS section sometimes create new Customer Records and Logins by mistake using the NEW CUSTOMER section.  Also this poses a security issue because if someone registers as a new customer then it gives them a password and access, which we do not want.

Any ideas on how to lock it or just plain remove it to only show the RETURNING CUSTOMERS login section?

Thanks,

Andy