Illegality is one of the conditions for a crime. This condition is the most important level of connections betweencriminal law and other branches of law. These relationships are weaker in terms of mala in se, which violates thebasic principles of interpersonal relations, while they are stronger in terms of mala prohibita, which violates detailednormative regulations. As a rule, this group includes tax crime, regardless of whether fiscal penal law orcommon criminal law is applied (the latter concerns VAT fraud and invoice forgery). In both cases, the basis forcriminal liability is a violation of tax law regulations (tax illegality). As a rule, tax law eludes the intuitive understandingof illegality (denial of legality). The main part of tax law provisions regarding the construction of taxesand the assessment of tax liability does not contain typical prohibitions or orders, but regulates the effects ofprivate law transactions, and the source of tax illegality will be the difference in views on the interpretation of theprovision between the taxpayer and the tax authority or administrative court. To the extent that the tax authoritydoes not issue a decision determining the tax liability (tax arrears), there is a presumption of the correctness ofthe tax declaration, which calls into question the authority of the criminal court to adjudicate a tax offense (to theextent that the statutory features of a prohibited act include incorrect declaration of tax).