This article analyzes the powers of tax authorities to conduct such control (supervisory) activities as test purchases when overseeing the use of cash registers. It substantiates the need to harmonize tax legislation and legislation on state control (supervision). It emphasizes the need to amend the legal regulation of test purchases and include them within the scope of tax legislation, which corresponds to their essence – control over the formation of the tax base by taxpayers through the use of cash registers. The relationship between test purchases and verification activities conducted as part of operational investigative activities is also discussed.