Basically internal control is for managerial assessment and corrective action while tax audit is conducted as a legal requirement. Strong internal controls may facilitate tax audit to a large extent. But still, the objectives of both are different. Tax audit is done for assessment of tax (particularly income tax) while internal control is applied to make the system work smoothly. It also detects the abnormalities if committed..

Basically Internal control is a mechanism by which target are set and actual performance are assessed with the said target in order to achieve organizational objective. Whereas, tax audit is an examination of tax paid whether the said amount of tax are accurate or not. 

In developed countries, large corporations are subject to frequent scrutiny by tax authorities. "Tax" includes not just income taxes but also value-added taxes, commodity taxes, royalty payments and other government levies. All of these categories are subject to tax audits. 

Because their transactions are so numerous and complicated, both the companies and the tax auditors must rely on strong internal controls to ensure that information is classified and recorded properly for tax purposes. When internal control is strong, tax audits can be done efficiently, without undue disruption to the companies' operations. When internal control is weak, the auditors must seek additional information. The companies bear the costs of producing this information in a credible format. Such costs can be huge if the internal control system is in disarray; indeed, a tax audit may be so invasive as to threaten a company's continuing existence. 

So investing in strong internal control is efficient for both operational purposes and for tax reporting purposes. For operational purposes, strong internal control ensures that resources are obtained and used efficiently and effectively in accomplishing organizational objectives. For tax purposes, strong internal control ensures that information is classified and recorded properly in fulfilling the organization's obligation to government bodies. 

Dear professor Daniel, 

Thank you  so much for this  explanation 

The relationship of tax audit and internal control is based only in the information disclosure by internal control to serve  tax audit. In this case it is the  contradiction between the role of  internal audit and a tax audit   

According to you what is  the feasible context  for this study?

I suggest Daniel Thornton's answer above is comprehensive.  There is no contradiction between internal audit and tax audit as they are conducted for different purposes. 

Thank you  for you  viewpoint  Pr.Chris Kelly, 

Please coud you offers new line of research on auditing