A 2011 paper found that both pro- and anti-immigration special interest groups play a role in migration policy. "Barriers to migration are lower in sectors in which business lobbies incur larger lobbying expenditures and higher in sectors where labor unions are more important." A 2011 study examining the voting of US representatives on migration policy suggests that "representatives from more skilled labor abundant districts are more likely to support an open immigration policy towards the unskilled, whereas the opposite is true for representatives from more unskilled labor abundant districts."