The Impact of the Product Market Competition on Tax Avoidance of the Firms Listed in Tehran stock Exchange

In this paper, the impact of the product market competition on tax avoidance of the firms listed in Tehran Stock Exchange is investigated. The index used to tax Avoidance is effective tax rate and indexes used to competition are the entry of cost and Herfindahl Indexes. The study sample consists of 78 Firms listed in Tehran stock Exchange during 1384 to 1390. In order to test the research hypothesis, Ordinary Least Squares regression has been used. The results showed that there is a meaningful and negative relation between entry of cost index and effective tax rate. But there is no meaningful relationship between Herfindahl Index and tax evasion.