WASHINGTON (USA TODAY) - Union membership in the USA dropped half a percent in 2012 to levels not believed to be seen since the 1930s, driven largely by a decline in the number of government employees who are union members.

The Bureau of Labor Statistics on Wednesday released its estimates of union membership for this past year based on the Current Population Survey, a monthly sample of 60,000 households nationwide.

It found the percentage of wage and salary workers who were members of a union declining from 11.8% in 2011 to 11.4% last year. It estimated that 14.4 million workers belonged to a union.

California continued to lead the nation in terms of union members with 2.5 million. New York had the highest percentage of workers belonging to a union, at 23.2%. North Carolina had the lowest percentage at 2.9%.

Michigan, where Gov. Rick Snyder signed a set of bills in December limiting the rights of unions in the state, remained in fifth place nationally, despite the loss of 42,000 union represented workers year to year; 16.6% of wage and salary workers there belonged to a union in 2012.

Other cash-strapped state and local governments laid off workers, many belonging to unions and, as in Michigan, limited collective bargaining rights. Total union membership fell by about 400,000 workers with more than half the loss - about 234,000 - coming from government workers including teachers, firefighters and public administrators.

Overall, union membership rates declined in 34 states, rose in 14 others as well as the District of Columbia and remained unchanged in two.

It is the lowest since the U.S. Bureau of Labor Statistics began estimating data on wage and salary workers in 1983, when union membership was 20% and union workers numbered 17.7 million people. A Congressional Research Service report from 2004 suggests the rate is the lowest since sometime in the 1930s.

"To employers, it's going to look like the labor movement is ready for a knockout punch," said Gary Chaison, professor of industrial relations at Clark University in Worcester, Mass. "You can't be a movement and get smaller."

Unions have steadily lost members since their peak in the 1950s, when about 1 of every 3 workers was part of organized labor.

• In Wisconsin in 2011, Gov. Scott Walker signed a law eliminating most union rights for that state's government workers. The state lost about 46,000 union members last year, mostly in the public sector.
• In Indiana, where a new right-to-work law took effect in March, the state lost about 56,000 union members. The law prohibits unions from requiring workers to pay union fees, even if they benefit from a collective bargaining agreement. Michigan lawmakers approved a similar measure in December.
• In Michigan, it now is illegal to require workers to make financial contributions to a union as a condition of employment, making the state the nation's 24th right-to-work state. Groups already have lined up to battle against the law, which was quickly passed during a lame-duck session of the state Legislature.

According to the Bureau of Labor Statistics, the public sector continued to have a much higher union-membership rate - 35.9% - than those of private-sector workers, at 6.6%. Workers in education, training and library services have the highest unionization rates, at 35.4%.

However, government rates of union membership saw the steepest drops from 2011 to 2012. About 8.3 million government workers, 37% of the total, were union members in 2011 and that number fell to 7.3 million, or 35.9% of the total, last year. The vast majority of those remained in local government where membership rates are still more than 40% of the total.

In manufacturing, 1.3 million workers - 9.6% of the total - were union members, down from 1.4 million workers, or 10.5% of the total, a year ago.

Among full-time wage and salary workers, union members in 2012 had median weekly earnings of $943, while those who were not union members earned $742.

Another problem for unions is an aging membership not being replaced with younger members. By age, the union-membership rate was highest among workers age 55 to 64, 14.9%, and lowest among those 16 to 24, 4.2%.

Despite the steady membership decline, unions remain a potent political force because of the money they spend helping union-friendly candidates seeking public office. Unions spent more than $400 million during the 2012 election cycle to support President Barack Obama's re-election, keep a Democratic majority in the Senate and help state and local candidates.

But as more governors and state lawmakers target unions, labor leaders have been forced to spend more money fighting political skirmishes and less on organizing new members.

"Organizing is very expensive, and it gets fought now in the public sector as well as in the private sector," said Barry Hirsch, a labor economist at Georgia State University.

Dwindling membership means unions carry far less influence than they used to in setting a benchmark for wages and benefits at nonunion companies. Unions already are gearing up to defeat Republican governors in Florida, Michigan, Ohio, Pennsylvania and Wisconsin, where they fear more anti-union measures could crop up soon.

Union officials blame membership losses on the lingering effects of the recession, as well as GOP governors and state lawmakers who have sought to weaken union rights.

"Our still-struggling economy, weak laws and political as well as ideological assaults have taken a toll on union membership, and in the process have also imperiled economic security and good, middle class jobs," AFL-CIO President Richard Trumka said.

Contributing: The Associated Press

Todd Spangler, Detroit Free Press