Immigration is one of the most hotly debated policy issues in the United States today. Despite marked divergence of opinions within political parties, several important immigration reforms were introduced in the post 1965 era. The purpose of this paper is to systematically analyze the drivers of congressional voting behavior on immigration policy during the period 1970-2006, and in particular, to assess the role of economic factors at the district level. Our findings provide robust evidence that representatives of more skilled labor abundant constituencies are more likely to support an open immigration policy concerning unskilled labor. Thus, a simple factor-proportions-analysis model provides useful insights regarding the policy making process on one of the most controversial facets of globalization.