BIR Audit Defects That Can Void a Tax Assessment

Start with audit authority

The Letter of Authority, or LOA, grants the designated revenue officers authority to examine the taxpayer’s books and records. The Supreme Court has treated it as the instrument issued by the Commissioner of Internal Revenue or a duly authorized official for that purpose. An examination without the required authority may affect the validity of the assessment.

Keep the LOA as received and identify each officer named in it.

Then check who actually examined the records.

Pay particular attention if the officers handling the audit changed while it was ongoing.

Check any officer change

In CIR v. McDonald's Philippines Realty Corporation, an LOA named officers for the taxpayer’s 2006 audit. After one officer was transferred, another continued under a referral memorandum without a new or amended LOA naming the substitute. The Supreme Court held that this unauthorized substitution violated due process, usurped the statutory grant of audit authority and invalidated the resulting assessment.

A personnel change does not automatically defeat an assessment. Establish what changed and what authority was issued.

Who was named in the original LOA? Was anyone reassigned? Who requested documents, conducted conferences, prepared findings, or continued the examination? Was a new or amended LOA issued? What dates appear on those documents?

Record these details while the audit is ongoing. Reconstructing them years later during CTA litigation may be difficult.

There is another caution. A strong procedural objection is not a substitute for developing the record. In Commissioner v. Marily Development Corporation, the Supreme Court stressed that the CTA's authority to decide issues not raised by the parties is not unlimited and that prescription, in particular, is a defense whose factual basis must be established by the taxpayer.

The 2026 replacement-eLA qualification

RMC No. 14-2026 clarifies that a replacement eLA may maintain audit continuity where the original authority was valid and the taxpayer, taxable period and scope remain unchanged. The Single-Instance Audit Framework operates prospectively; it does not automatically invalidate earlier LOAs. A properly authorized replacement is different from an officer continuing an audit without the required authority.

The BIR also states that a challenge to a replacement eLA does not itself suspend the audit. Preserve the objection, identify the specific defect and continue protecting all response and protest deadlines.

Prove service

Tax assessments also depend on proper notice.

In Fort 1 Global City Center, the Supreme Court affirmed the cancellation of deficiency assessments where the BIR failed to establish proper service of its notices. The Court emphasized requirements governing delivery to the taxpayer or a duly authorized representative and found that delivery to persons whose authority or relationship to the taxpayer had not been established did not satisfy the required process. The taxpayer's later protests did not cure the defective service.

The company also needs a clear process for receiving BIR correspondence.

Identify who is authorized to receive notices, where receipt is logged, who keeps the envelope and proof of delivery, and when tax and legal personnel must be informed. Consider how documents received by guards, receptionists, administrative staff, branches, shared-office staff or service providers reach the responsible person.

A service dispute requires evidence. The taxpayer also risks losing response time if a validly served notice remains unnoticed in the office.

The conclusion in Fort 1 depended on the evidence and the service rules applicable to the notices. It does not mean that every receipt by a guard or employee is automatically invalid; prescribed substituted service may be available if its requirements are met. Preserve the BIR registration and address-change records, delivery details, identity and authority of the recipient, and any service attempts. A corporation should not rely solely on its SEC GIS to establish its BIR-registered address.

Prove prescription

Under Section 203 of the Tax Code, the ordinary assessment period is three years from the statutory filing deadline or actual filing, whichever is later. A return filed early is treated as filed on the prescribed deadline. This is not simply three years after the taxable year ends.

Section 222(a) provides a ten-year period from discovery in specified cases of a false or fraudulent return with intent to evade tax, or failure to file. Valid waivers and statutory suspension rules may also affect the calculation. Assessment and collection periods must be examined separately.

In CIR v. Arturo E. Villanueva, Jr., the BIR invoked the ten-year period based on alleged substantial underdeclaration, but the assessment notices did not explain that invocation and the returns and financial statements did not establish the claimed undeclared sales or fraud. The Court held that an error alone does not justify the extraordinary period: the required false or fraudulent return basis and due process must be established.

The prima facie rule under Section 248(B) is rebuttable. For sales, receipts or income, the statutory comparison concerns the unreported amount exceeding 30% of the amount declared; for deductions, it concerns the overstatement exceeding 30% of actual deductions. These are not interchangeable denominators. Nonfiling is a separate statutory ground and should not be conflated with an allegedly inaccurate return.

CIR v. Marily Development Corp. is a caution against assuming a taxpayer victory from missing BIR evidence alone. The Supreme Court reversed the blanket cancellation and remanded the case, while recognizing assessments proved to be prescribed. The taxpayer needed readable returns and proof of filing to establish its own prescription defense. The CTA’s power to address unraised issues is limited by the evidentiary record.

Build a separate chronology for each return and tax period: statutory due date, actual filing, assessment dates and dispatch evidence, waivers and claimed suspensions. An asserted defect should be pleaded and supported while procedural remedies remain open.

Keep procedure and merits alive

A procedural objection should be developed alongside the substantive tax defense.

I suggest keeping two files and preparing them at the same time.

The first is the merits file: returns, ledgers, invoices, contracts, withholding documents, reconciliations, tax opinions, transfer-pricing support, and factual explanations for the transactions under examination.

The second is the audit-validity file: the LOA and amendments, names of authorized officers, dates of examination, requests for documents, proof of service, registered address records, PAN and FAN or FLD documents, filing records, waivers, protests, and evidence relevant to prescription.

This keeps the evidence on the assessed amount separate from the evidence on audit validity, so both receive attention before litigation.

A 2026 reminder about closure notices

In CIR v. Elric Auxiliary Services Corp./Sacred Heart Gas Station, G.R. No. 226945, 19 February 2026, the Court rejected the use of closure-related VAT notices as substitutes for a valid deficiency assessment and recognized the CTA’s jurisdiction over “other matters” arising under the Tax Code. The ruling is fact-specific. It does not make all closure notices void or allow a taxpayer to disregard an ordinary assessment protest deadline.

Build the record early

Document a possible audit defect while the relevant records and witnesses are still available.

For a business owner, CFO or tax head, the amount assessed is one part of the review.

Also establish the following:

Who was authorized to examine the records? What was served, who received it and when? When did the assessment period begin and end? What evidence supports the BIR’s position? Which objections and deadlines require action now?

The defense may turn on the computation, audit authority, service of notices or prescription. Review each issue against the actual documents and procedural history.

Keep the evidence as events occur rather than assuming it can be reconstructed later.