Union members from around the country rally at the Michigan State Capitol to protest a vote on Right-to-Work legislation Dec. 11, 2012 in Lansing, Mich. - 

Today's news from the Bureau of Labor Statistics won't surprise you: Union membership fell last year. According to the BLS, the percentage of American workers who belong to a union dropped to 11.3 percent from 11.8 percent. That may not sound like much but economists say for a single year, it's significant. Union representation in the American workforce hasn't been this low since the 1930s.

New anti-union laws in industrial states like Michigan and Wisconsin haven't helped. Just yesterday Pennsylvania became the latest northern state to consider "right-to-work" legislation.

The recession has hurt unions too. 35.9 percent of public-sector workers are unionized. That compares to just 6.6 percent in the private sector. But the new data shows the number of unionized public employees has dropped, the victim of state and city budget cuts.

But labor economist Paul Harrington at Drexel University says labor's real problem isn't Republicans or recessions. It's the kind of jobs the American economy is creating. "A lot of the industries where we're getting job growth are in non-union areas and non-union occupations," Harrington says.

While manufacturing, a traditional union stronghold, has declined over the past three decades, the service sector has risen. Harrington says right now finance, leisure and hospitality, and retail are among the growing job sectors in the U.S, industries that aren't generally unionized or have resisted unions.

Gary Chaison, a labor specialist at Clark University in Massachusetts, says that means unions can't "count on prosperity" to replenish the members they've lost over the years. "And you can add to this the fact that when the unions decline in size they become increasingly seen as irrelevant to our society and on the margins of our society and economy," Chaison says.

Labor experts say many younger workers may see unions that way, especially the growing numbers who change jobs frequently or do temp, part time or contract work, Labor advocates are urging unions to spend more money figuring out ways to recruit these new workers. Organized labor is already spending more money to fend off anti-union legislation in states like Michigan and Pennsylvania.

Follow Sarah Gardner at @RadioGardner