The article aims to verify whether the principle of two-tier proceedings is infringed where in the assessment decision issued in the appeal proceedings, case facts are qualified under the law differently than in the first-instance decision — whereby the substantive legal grounds of the resolution are changed. "Tax case" resolved in the assessment decision is to fix or determine the amount of tax liability. Therefore, change in legal qualification of the case facts and, as a consequence, in the substantive legal ground of the appeal resolution, does not bring about the change of the tax case — i.e., the loss of its identity. Such decision of the appeal authority does not infringe the taxpayer's constitutional right to appeal or the principle of two-tier proceedings.