An additional levy of one hundred percent of the business license tax now being assessed to and paid by all businesses within the boundaries of the parking and business improvement area as designated in Section 21B-9 is hereby imposed; provided, however, the initial additional levy to be paid is established as sixty-six and two-thirds percent of the business license tax now being assessed to and paid by all such businesses based upon the business license tax paid and/or payable of record as of August 15, 1976. Payments of a similar levy of any businesses which are now exempt under the Constitution of California from payment of a business license tax shall be on a voluntary basis. (Ord. No. 1661 (NCS), § 3.)