The Congressional Research Service (the research arm of Congress) released a study last week on Right to Work Laws. You can get to the report here: http://www.fas.org/sgp/crs/misc/R42575.pdf
The Congressional Research Service produces a variety of papers on current issues of legislative importance. These reports are succinct and well-cited. Until relatively recently, they have remained unavailable to the public (libraries included). No one location will have them all: