The article examines the problem of administrative discretion of a tax authority in the context of mediation of tax disputes. The limits of discretion determined by the imperative nature of tax legislation are analyzed. The conflict between the public interest and the need for compromise is revealed, generating risks of taxpayer inequality and abuse. It is argued that the absence of legalized criteria makes mediation fictitious. Ways of legislating a closed list of permissible concessions and procedural guarantees are proposed.