According to a study by the National Institute of Labor Relations Research (the NILRR), the bulk of the country's job growth since the end of the recession in 2008 took place in right to work states. Right to work states have some form of limitation on the ability to make paying union dues a condition of employment. The NILRR analyzed data provided by the Bureau of Labor Statistics and found that approximately 72 percent of the net job growth in the United States from June 2009 through November 2012 was in the 21 right to work states in the United States (the job-growth numbers do not include Indiana, which only recently became a right to work state). These 21 states account for only 38.8 percent of the population.
According to the NILRR, “if these [right to work] states’ job increase had been no better than the 0.85 percent experienced by forced-unionism states as a group, the nationwide job increase would have been less than half as great.”
According to the American Enterprise Institute (AEI) adjusting for population, the right to work states had 4 times the job growth as the non-right to work states. The full NILRR post on this subject can be found here. The AEI's analysis can be found here.