The purpose of this paper is to extend Ethier’s model and to explore some issues not considered in his work. First, we consider a two-by-two Heckscher-Ohlin model in which the production functions are subject to variable returns to scale, and examine the economic effects of internal enforcement on illegal workers. Second, we use Mayer’s model to analyze the long run and short run effects of enforcement policy. Third, we apply Chavas’ work to compare the relationships between long run and short run economic effects. It shows that the external output effects caused by variable returns to scale production functions are crucial in determining income and other economic effects. Under certain circumstances, it may even make income increased and long run income effect greater than its short run effect.