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

Union protestors crowded the capitol, but Michigan lawmakers swiftly approved legislation yesterday making Michigan a so-called "right-to-work" state.

Employees in the state in unionized workplaces can freely opt out of union membership and the union fees they would otherwise have had to continue to pay.

Michigan is the 24th state to pass such a law, and more states could follow, according to Harley Shaiken, a labor economist at U.C. Berkeley.

"I think we're going to see a battle nationally," he says. "I think more states might be emboldened by what took place in Michigan."

He's quick to add, however, that the battle isn't over in Michigan yet either. "How that plays out could influence what happens to right-to-work in other states."

Follow Jeff Horwich at @jeffhorwich