CHICAGO (Reuters) - The percentage of workers represented by a union dipped slightly in 2011, the Bureau of Labor Statistics said on Friday, as organized labor came under attack in states once considered union strongholds, including Wisconsin and Ohio.

In 2011, 11.8 percent of U.S. workers were represented by a union, the BLS said, down from 11.9 percent in 2010 and compared to a peak of 28.3 percent of the workforce in 1954.

Strip out government workers, where 37 percent of the work force nationally is unionized, and union penetration of private industry was just 6.9 percent in 2011, unchanged from 2010.

The total number of union members actually grew slightly last year, to 14,764,000 from 14,715,000 in 2010. But the number of workers represented by organized labor remained steady while the overall number of workers employed in the economy grew, the BLS said.

The number of unionized workers in Wisconsin fell nearly 6 percent in Wisconsin last year, to 358,000 from 380,000, the BLS said, as Republicans passed controversial curbs on the bargaining rights of public sector workers. That bitter debate spurred the largest street marches in Madison since the Vietnam War and two rounds of recall elections so far.

Only 14.1 percent of the state's workers were unionized at the end of 2011, the BLS said, down from 15.1 percent in 2010.

But in other Midwest states that have been battlegrounds for organized labor, the picture was more mixed, the BLS said.

In Indiana, which is poised to enact a right-to-work law banning unions from collecting mandatory dues from workers, union representation actually grew last year, the BLS said.

In 2011, 333,000 workers in the state were represented by a union, up from 313,000 workers in 2010. As a result, 12.4 percent of the state's workforce was union represented in 2011, up from 12.2 percent in 2010.

In Ohio, where an effort to impose union curbs on public workers similar to Wisconsin's was overturned by voters in a November referendum, the percentage of workers represented by a union remained unchanged at 14.7 percent.

The BLS said the highest union penetration rate in 2011 was in New York state, where 24.1 percent of workers were members of a union, followed by Alaska with 22.1 percent of the workforce unionized and Hawaii with 21.5 percent.

The BLS said union presence was weakest in North Carolina, where just 2.9 percent of workers were union members, followed by South Carolina (3.4 percent) and Georgia (3.9 percent).

(Reporting by James Kelleher. Editing by Peter Bohan.)

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