This research examines the impact of occupational choices and tax evasion on the tax administration policy in a hierarchical tax model. The economy has two sectors, wage-earners and self-employment, with evasion only possible in the latter. Incorporating occupational decisions produces a smaller marginal tax rate and a larger budget for the IRS. However, the resources are still insufficient to audit all self-employed, resulting in distortions in occupational choices favoring self-employment. These distortions prevent production efficiency from achieving the optimum level, indicating that the Diamond-Mirrlees theorem is not applicable in this context. Finally, applying differential taxation represents a Pareto improvement, but it results in higher taxes for self-employment.