For enterprises engaged in banking, insurance, and trust investment, the sales amount from operations not within the scopes of their exclusively authorized business, as defined in the footnote of "Time Limit for Issuing Sales Documentary Evidence" of this Act, may apply to calculate business tax in accordance with the provisions in Section 1 of this Chapter and file tax returns in accordance with the provisions of Article 35. 
Where application has been made in accordance with the preceding paragraph to calculate the amount of business tax under Section 1 of this Chapter, application may not be made for alteration for three years following approval. 
The Ministry of Finance may gauge the nature and capabilities of small business entities and determine that Section 1 of this Chapter shall be applied to calculate business tax and Article 35 shall be applied to file tax returns and pay taxes.