In the field of tax law, the audit procedure constitutes one of the essential pillars to guarantee the correct determination of tax obligations and, at the same time, the protection of the taxpayer's rights. In this context, a rigorous scrutiny of the actions of the Tax Administration is indispensable, not only from a substantive perspective, but also from the strict observance of the legally established procedure. The legality of the auditing act cannot be evaluated only in terms of the results obtained, but also considering the formal regularity of the process followed to achieve them. This perspective is crucial when discussing the validity of administrative acts issued on the basis of actions that may have violated essential stages of the procedure.
A recent jurisprudential development has reaffirmed the importance of differentiating between procedural defects that affect the validity of an administrative act and discrepancies that deal with the merits of the tax matter. This distinction has substantial implications. For example, when a taxpayer claims that the Administration acted outside the limits of the approved procedure -either by not following the due sequence, by modifying deadlines without valid notification or by using procedures other than those legally established-, we are dealing with a possible formal infringement that may lead to the nullity of the acts issued. On the contrary, if what is alleged is a misinterpretation of the facts or of the applicable rule, without there being a breach of procedure, then we are faced with a substantive dispute that must be resolved through a technical analysis, not through its formal annulment.
This criterion makes it possible to establish a rational and coherent order in the audit and challenge process. It avoids the use of formal allegations as a strategy to avoid the substantive debate and reinforces the principle that administrative proceedings must be subject to the rules expressly set forth in the tax and administrative regulations. Thus, taxpayers must clearly identify which aspects of the procedure are being questioned and by what means they must be resolved. This provides predictability, avoids unnecessary dispersion of resources and strengthens legal certainty.
Another fundamental aspect is the respect for the limits of action of the Administration in the qualification of economic facts. The auditing power must be exercised within the exclusive framework of the tax regulations, without projecting itself on legal effects of another nature or extending to fiscal years other than the one under review. The Administration may verify the economic substance of the acts declared by the taxpayer and determine whether or not they generate tax obligations, but it must do so within the parameters of legality, temporality and competence that govern its actions.
This becomes particularly relevant when an attempt is made to extend the effects of an assessment made in a given year to other periods not audited, or when an attempt is made to attribute liabilities to third parties on the basis of facts that have not given rise to specific and enforceable tax obligations. This type of extrapolation violates basic principles such as legality, the non-retroactivity of tax legislation and respect for the limited purpose of the audit.
Likewise, when the Administration formalizes a definitive audit, all subsequent actions must be adapted to this new nature. Issuing requirements under a partial audit after a definitive procedure has been validly initiated constitutes a violation of the legal procedure that invalidates such actions. In accordance with the principle of causal connection between administrative acts, if the initial act is vitiated, so are those acts that depend directly on its validity. This nullity may extend to the results of summons, determination resolutions or fines, provided that they are related to previous irregular acts. However, the principle of preservation of the acts must also be applied, which implies maintaining those contents that are independent and not affected by the defect.
In relation to changes in the audit staff during the procedure, it is important to note that these are part of the discretionary power of the Administration, and do not constitute an infringement by itself. Only if it is proven that such change violated the taxpayer's right of defense could it be considered as an infringement of due process.
In the same way, the correct notification of the acts is only a part of the formal compliance. Respecting the deadlines and the logical sequence of procedural acts has a direct impact on the guarantee of the taxpayer's right of defense. The issuance of acts outside the established deadlines or the extension of requirements through untimely communications constitutes a violation of the legal procedure and, consequently, may lead to their nullity, in accordance with the provisions of the rules on general administrative procedure.
In short, the audit procedure must be understood as a process that ensures both the legitimate power of the Administration to verify compliance with tax obligations and the guarantee for the taxpayer to be treated in accordance with a clear, predictable and legally structured regulatory framework. The administrative action must be strictly subject to the legal procedure from the beginning until the issuance of the final act, since any deviation compromises its legitimacy and violates the balance that must exist between the public interest and individual rights. The legality of the procedure does not admit exceptions or informal practices: it is the cornerstone on which all auditing actions that aspire to be valid and respectful of the legal order must be built.
