The research on the topic «Constitutional and legal restrictions on legal experiments in the tax sphere: principles of equality of taxpayers and voluntary participation» is conditioned by the need for a theoretical understanding of the criteria for the permissibility of legal experiments in the tax sphere that have not found their way into the legislation of the Russian Federation. The author uses methods of analysis and synthesis, as well as the formal legal method to study the provisions of the Constitution of the Russian Federation, the Tax Code of the Russian Federation, and regulatory legal acts that regulate the procedure for conducting legal experiments in other branches of legislation. The author evaluates the relationship between experimental legal regulation in the tax sphere and the prohibition of coercion to participate in experiments established by the Constitution of the Russian Federation, the principle of equality, and the principle of the inadmissibility of restricting rights except on the basis of federal law and for constitutionally significant purposes. The author defines what requirements for legal experiments in the field of taxation follow from the content of the principle of equality and universality of taxation. As conclusions to the article, the criteria that, as a general rule, must comply with the federal law on conducting a tax experiment are formulated: the prohibition of worsening the taxpayer's situation and the prohibition of coercion to participate in a legal experiment.