An eligible small business, as defined in Section 44 of the Internal Revenue Code, shall be allowed a credit against the tax otherwise due pursuant to chapter 143, not including sections 143.191 to 143.265, in an amount equal to any amount paid by the eligible small business to the United States Small Business Administration as a guaranty fee pursuant to obtaining Small Business Administration guaranteed financing and to programs administered by the United States Department of Agriculture for rural development or farm service agencies. No tax credits provided under this section shall be authorized on or after the thirtieth day following the effective date of this act^*. The provisions of this subsection shall not be construed to limit or in any way impair the department’s ability to issue tax credits authorized prior to the thirtieth day following the effective date of this act^*, or a taxpayer’s ability to redeem such tax credits.