Ruth Milkman's Report Featured in The Nation
According to a study conducted by Ruth Milkman New York remains the most union dense state.

How Did New York Become the Most Unionized State in the Country?
The Nation, 9.3.14
According to a study conducted by Ruth Milkman and Stephanie Luce, City University of New York researchers, New York remains the most union dense state in the country at 24.6 percent of workers (article links to the GC press release)