National Internal Revenue Code (NIRC)
Section 233. Subsidiary Books. - All corporations, companies, partnerships or persons keeping the books of accounts mentioned in the preceding Section may, at their option, keep subsidiary books as the needs of their business may require: Provided, That were such subsidiaries are kept, they shall form part of the accounting system of the taxpayer and shall be subject to the same rules and regulations as to their keeping, translation, production and inspection as are applicable to the journal and the ledger.