The percentage of U.S. workers belonging to unions tumbled to 11.3 percent in 2012, the lowest percentage in 76 years, led by dramatic declines in states where lawmakers have put organized labor in the political crosshairs, government figures showed on Wednesday.
The total number of union members fell by nearly 400,000, from 11.8 percent of the workforce in 2011, the Labor Department report on union membership said. The rate of 11.3 percent of the workforce was the lowest since 1936, when Franklin Roosevelt was president.
Almost half the losses in the last year were in the industrial Midwest -- Indiana, Wisconsin, Ohio and Michigan -- where states with Republican-led governments have led an assault on unions.
Indiana passed a so-called "right-to-work" law in February, 2012 making payment of union dues voluntary for workers. Wisconsin passed severe restrictions on public sector unions in 2011, but they were blocked by the courts for part of 2012.
Ohio also passed curbs on public sector unions in 2011, but they were overturned by referendum the same year. Michigan last month passed a right-to-work law that has not yet taken effect.
Robert Bruno, professor of labor relations at the University of Illinois, said a growing number of laws that make organizing workers more difficult were part of the reason for "an incremental erosion" of the labor movement.
"It goes back a couple of decades, that there has been a growing number of anti-labor policies," Bruno said. "We have the weakest labor law and enforcement of labor law in the entire Western industrialized world," he said.
Some of the most brutal fights over collective bargaining have taken place at the state level. A federal appeals court last Friday upheld a controversial Wisconsin law restricting the power of public-sector unions.
Last year, organized labor also suffered big membership losses in states considered union strongholds and controlled by Democrats, including Illinois and New York. Lawmakers grappling with public employee pension crises and sharp drops in tax revenue have sought concessions from public workers.
"It reflects a number of things beyond labor's control, such as the state of the economy," said Harley Shaiken, labor relations professor at the University of California at Berkeley. (Read More: The 10 Least Stressful Jobs)
"It used to be big labor and big business. Now we have small labor and big business," he said.
On the other hand, unions made strong gains in traditionally weak states for organized labor, including Georgia, Kentucky, Louisiana, Oklahoma and even Texas, due to booming local economies.
Some analysts blame unions for the drop. Membership has been falling since 2008, when it was 16.1 million, or 12.4 percent of the workforce, federal data shows. It peaked in 1954, when 28.3 percent of workers were represented by organized labor.
"They must now admit that they are not investing enough staff and funds in organizing and not embarking on an imaginative journey to rediscover the relevancy of unions," said Gary Chaison, professor of industrial relations at Clark University. "Essentially, workers are feeling tremendous job insecurity ... Yet as today's figures suggest, workers are not turning to unions to act as their voice."
The report also showed full-time unionized workers had median weekly earnings of $943, 27 percent more than the $742 of those whose pay was not collectively bargained.
The activist group Center for Union Facts, which is critical of the labor movement, said unions have made salary and benefit demands that have hurt the budgets of corporations and the public sector.
Slow recovery from the 2007-09 recession has hurt revenues of state and local governments, forcing them to eliminate jobs and to cover the swelling costs of healthcare and pensions by cutting spending in other areas.
"It's not a secret that some politicians chose to cut public education funding, balance the budgets on the backs of students and slash the education workforce," Dennis Van Roekel, president of the National Education Association, a 3 million member union, said in a statement on the report. (Read More: For Americans, 'Cope' Has Replaced 'Hope': NBC Poll)
In 2012, public sector unions lost 234,000 members. Nearly 80 percent of that decline was in organizations representing local government workers, primarily teachers. More than a third, 35.9 percent, of public-sector workers belonged to unions, compared with just 6.6 percent of those in the private sector.
From December 2007, near the start of the recession, to December 2012, state and local governments shed 489,000 jobs.
"That's a highly unionized sector and we know the public sector has been doing poorly in this recovery," said William Briggs, chief economist for the largest U.S. union, the AFL-CIO, and former undersecretary at the U.S. Labor Department. "The weakness isn't just a union story. It's a story about the economy not functioning the way we hope it would."
He noted the age group with the lowest membership rate - only 4.2 percent for workers aged 16 to 24, compared with 14.9 percent for those aged 55 to 64 - was also the one struggling most to find full-time jobs.
Black workers had the highest union membership rate, at 13.4 percent, followed by whites at 11.1 percent, Hispanics at 9.8 percent and Asians at 9.6 percent. Black men alone had a rate of 14.8 percent, as African-American women mostly hold public jobs, Briggs said.
Women made up 57 percent of the public sector workforce in 2012 and accounted for 72 percent of the union membership decline, the National Women's Law Center said.