Last year, the number of union members in the U.S. fell by more than 400,000, or 2.7%. This decline was just a drop in the bucket compared to the long-term collapse of organized labor over the past several decades. In the past few years, states like Wisconsin and Michigan have passed legislation like “right-to-work” laws and even banned collective bargaining, further undermining public and private unions.

Unionization in this country varies widely from state to state. In places like New York and Alaska, more than 20% of workers were union members in 2012. In states like Arkansas and North Carolina, the number was closer to 3%. The concentration of unions in states has a lot to do with their employment base and political atmosphere. But one thing is clear, only seven states have seen the percentage of workers in unions increase in the past 10 years, and things are not looking up for organized labor. Based on data collected by the Bureau of Labor statistics and calculations by Unionstats.com, 24/7 Wall St. identified the states with the strongest and weakest unions.

Click here to see the 10 states with the strongest unions

Click here to see the 10 states with the weakest unions

Late last year, Michigan, one of the most unionized states in the country, passed right-to-work legislation. It thus became the 24th state in the country to make it illegal for employers to require workers to join a union or pay dues. The widespread adoption of these laws threatens the long-term future of unions. All 10 of the states with the lowest union membership are right-to-work states. Only two of the 10 states with the highest union membership are right-to-work, and one of those is Michigan, which only passed its law in December.

The concentration of unions depends in part on the representation of government employees. While they make up a smaller segment of the workforce than the private sector does, public employees — including teachers, postal workers, police officers and firefighters — are much more likely to be union members. In New York, 1.35 million of the state’s nearly 8 million workers were in public sector jobs in 2012, and a nation-high 72% of those workers were in unions. A lack of public sector unionization can also dramatically affect a state’s overall rank. In North Carolina, the least-unionized state in the country overall, just 8.8% of public workers were union members.

The private sector is much less unionized. As of 2012, just 6.6% of the nation’s public workers were card-carrying members of organized labor groups. However, because the private sector is so much larger, concentration of unions in some industries can make a major difference. In states like Michigan and Illinois, more than 10% of employees in the private sector were in unions. A lot of this has to do with the composition of the state’s private sector. In Michigan, 18.4% of all jobs are in manufacturing, a traditionally highly unionized sector.

Both public and private sector union jobs have declined dramatically in recent years. According to Unionstats founder Barry Hirsch, different factors have impacted the public and private sectors. The decline of government union workers is more pronounced in places that were hit harder by the recession, needed to make budget cuts and had the political mandate to do so. In states such as Wisconsin and Michigan, Hirsch added, “the public unions have been very convenient political scapegoats.”

In the private sector, the decline has been more widespread in the past 10 years. In all but three states, the proportion of union workers in the private sector fell. The decline has been particularly pronounced in manufacturing, where millions of union and nonunion jobs have been lost. Between 2002 and 2012, the number of manufacturing jobs declined by 17.6% due to the replacement of blue-collar jobs by machines or outsourcing. Over the same period, the number of union workers in manufacturing fell by 45%.

Hirsch noted that as the economy recovers from each recession, job growth does not occur in union-heavy fields. “Jobs are constantly being destroyed and created,” he said, “and both union and non-union jobs are being destroyed, but you don’t see new union jobs being created, which results in a gradual, long-run process that erodes union membership and density.”

In order to identify the states with the strongest and weakest unions in 2012, 24/7 Wall St. used data from Unionstats.com, an online union membership and coverage database. The site, which analyzes Bureau of Labor Statistics’ Current Population Survey, provides labor force numbers and union membership in both the private and public sector, including manufacturing and construction. The rankings are based on the percentage of state workers who were union members, but we also refer to the percentage of workers covered by unions, meaning they are in a sector represented by unions, but are not themselves voting members. 24/7 also reviewed December 2012 unemployment rates for each state from the BLS, as well as income and poverty data for 2011 from the U.S. Census Bureau.

These are 24/7 Wall St.’s states with the strongest and weakest unions.