THE cornerstone of a fair tax system is due process. Taxpayers have the fundamental right to be informed in writing of the factual and legal basis for any tax assessment. Thus, proper service of assessment-related notices — including the Notice of Informal Conference, Preliminary Assessment Notice (PAN) and Final Assessment Notice (FAN) — is paramount, and failure to comply thereof renders the assessment void.

To streamline this process, the Bureau of Internal Revenue (BIR) enacted Revenue Regulations (RR) 18-2013, amending RR 12-99. These regulations outline the permissible methods of serving assessment notices.