§ 25-u. Construction. Nothing contained in this article shall be construed as reducing the amount of a receipt for sales tax purposes under any of the sales taxes imposed or authorized by article twenty-eight or twenty-nine of the tax law; or as reducing the gross receipts, the gross income or the gross operating income subject to tax pursuant to section one hundred eighty-six-a of the tax law or authorized to be subjected to tax by section twelve hundred one of the tax law. The burden of establishing eligibility to claim the benefits of this article shall rest with the party claiming such benefits.