National Internal Revenue Code (NIRC)
Section 13. Authority of a Revenue Offices. - subject to the rules and regulations to be prescribed by the Secretary of Finance, upon recommendation of the Commissioner, a Revenue Officer assigned to perform assessment functions in any district may, pursuant to a Letter of Authority issued by the Revenue Regional Director, examine taxpayers within the jurisdiction of the district in order to collect the correct amount of tax, or to recommend the assessment of any deficiency tax due in the same manner that the said acts could have been performed by the Revenue Regional Director himself.