The Inland Revenue Board of Malaysia (IRBM) provides a monitoring mechanism of corporate governance through tax audits. However, indicators associated with the tax authority monitoring system remain underexplored due to data confidentiality. This study aims to examine the indicators used by the tax authority in performing tax monitoring where the tax return data of firms that claim reinvestment allowance (RA) were employed alongside the historical audit data of corporate taxpayers of both a tax-monitored firm and an unmonitored tax firm. The results of the analysis reported that the tax authority monitoring system is closely associated with fundamental details disclosed in the tax return namely, assessment year, profitability, scale of operation, firm directorship, tax consultancy and industry type. In contrast, the incidents of tax avoidance and incentive utilisation indicators were not prominent in tax authority monitoring. The investigation of firms that experienced tax monitoring provides insight into indicators which interest tax authorities when it comes to a firm’s tax audit. This research revealed new evidence on IBRM preferred indicators in conducting tax monitoring.