According to the Kau and Rubin (K&R) hypothesis, increasing the government's power to collect taxes, through increased tax revenues, expand the public sector expenditure. In this regard, the main objective of this paper is to empirically test the relationship between government's power to collect taxes, tax revenues and government expenditures in Iran during the period of 1971-2013. For this purpose, rate of female participation in the labor market and self-employment rate is used as two variables which are the indicators of government's power to collect taxes, and Toda and Yamamoto granger causality method is used. The Results show no causality relationship from the government's power to collect taxes indicators toward government spending (Rejection of the Kau and Rubin hypothesis). The reason for this conclusion is justified based on the absence of causality relationship from government's power to collect taxes indicators toward tax revenue; however, the causality relationship from tax revenues toward government expenditure is approved (confirm of the Friedman's hypothesis). According to other results, the causal relationship from the oil revenues toward government expenditure and tax revenues is confirmed.