This study is aimed at studying the legal status of third parties in the system of tax relations, in particular, in the framework of tax disputes, to identify and disclose existing problems in the implementation of the rights and obligations of third parties. Based on the conducted research, it was concluded that the lack of a normative definition of the concept and status of third parties represents a significant defect in the current legal regulation. The author offers an original concept synthesizing doctrinal approaches with an analysis of the essence of third parties and their interest in tax legal relations. The article concludes that the regulation of the legal status of third parties is subject to improvement, taking into account the evolving judicial and arbitration practice and foreign experience. According to the author, this will make it possible to fully implement the constitutional principles of equality and justice by introducing clear criteria for the participation of such subjects (interest, risk of violation of rights, etc.) and expanding their procedural powers at the pre-trial stage of appeal.