The chapter aims to provide a robust classification of auditor modifications of financial and internal control assurance in the field of tax compliance and assess them from the point of view of the undertakings' tax risk and the current worldwide trend to increase tax compliance requirements. Based on the stakeholder theory, this chapter applies the coding of narratives in auditors' opinion modifications to cluster the reasons for modification within the tax compliance area. The chapter shows the insignificance of tax compliance matters in overall modification trends in US-based companies and confronts it with global trends in terms of increasing tax compliance requirements. The chapter adds to the current discussion on tax compliance by providing robust evidence on the enforcement deficiencies in a major global economy. The findings support the conclusion that enforcement of tax compliance through an agent remunerated by a private principal does not substitute the enforcement function of inland revenue. The current financial statements and internal control audit practice have limited impact on tax enforcement and therefore the indirect channel does not eliminate information asymmetry between tax authorities and companies and audits provide only infrequently credible signals of tax incompliance to tax authorities.