(a) Credit for primary taxes imposed under article thirteen, chapter eleven of this code. — A credit shall be allowed against the primary tax imposed by this article equal to the amount of the liability of the taxpayer for the taxable year for any tax imposed under article thirteen, chapter eleven of this code: Provided, That the amount of such business and occupation tax credit shall not exceed fifty percent of the primary tax liability of the taxpayer under this article, which is attributable to the West Virginia taxable income derived by the taxpayer for the taxable year from the business or occupation with respect to which said tax under article thirteen was imposed, and shall not in any event exceed fifty percent of the primary tax liability of the taxpayer under this article for such taxable year: Provided, however, That the entire amount of the business and occupation tax liability of the taxpayer, which was taken as a deduction in determining its federal taxable income for the taxable year, shall be an adjustment increasing federal taxable income under section six of this article: Provided further, That the taxpayer may at its option elect in lieu of claiming the credit allowable by this subsection, to not increase its federal taxable income under section six of this article and thereby take as a full deduction under this article for the taxable year the amount of its business and occupation tax liability for the taxable year, which was taken as a deduction on its federal return for such taxable year.

For purposes of this section, the tax imposed under article thirteen, chapter eleven of this code shall be the amount of the liability of the taxpayer for such tax under said article thirteen computed without reduction for the tax credit for industrial expansion or revitalization allowed for such year.

(b) Credit for taxes imposed under article twelve-a, chapter eleven of this code. — A credit shall be allowed against the primary tax imposed by this article equal to the amount of the liability of the taxpayer for the taxable year for any tax imposed on the taxpayer under article twelve-a, chapter eleven of this code: Provided, That the amount of such credit shall not exceed fifty percent of the primary tax liability of the taxpayer under this article which is attributable to the West Virginia taxable income derived by the taxpayer for the taxable year from any source with respect to which said tax under article twelve-a was imposed and shall not in any event exceed fifty percent of the primary tax liability of the taxpayer under this article for such taxable year: Provided, however, That the entire amount of the carrier income tax liability of the taxpayer, which was taken as a deduction in determining its federal taxable income for the taxable year shall be an adjustment increasing federal taxable income under section six of this article: Provided further, That the taxpayer may at its option elect in lieu of claiming the credit allowable by this subsection, to not increase its federal taxable income under section six of this article and thereby take as a full deduction under this article for the taxable year the amount of its carrier income tax liability for the taxable year, which was taken as a deduction on its federal return for the taxable year.

(c) Expiration of credits. — The credits, authorized in subsections (a) and (b) of this section, shall expire and not be authorized or allowed for any taxable year beginning after June 30, 1987.