Earlier this week, AFL-CIO President Richard Trumka said, "We've never seen the incredible solidarity that we're seeing right now."
Stern agreed. "I think there's an incredible degree of not just solidarity but appreciation that people are being attacked, and the one way that people who don't have as much power get power is by uniting their strength," he said.
But that may be more than just spin from two union heavyweights. Recent polling found that an overwhelming majority of Americans side with public workers in the battle over bargaining rights.
A New York Times/CBS News poll found that a majority (56 percent) of Americans also opposed cutting the pay or benefits of public employees to reduce state budget deficits.
But that does not necessarily mean that unions are popular (just a third of Americans had a favorable view of unions, according to the poll), only that Americans do not want their rights taken away.
"Public opinion has been much more favorable to unions and to workers rights -- it just seems like a political attack without a financial purpose," Stern said. "I think that's all been helpful."
Joe McCartin, a history professor at Georgetown University and the director of the Kalmanovitz Initiative for Labor and the Working Poor, said what is happening in Wisconsin has "caught almost everyone by surprise.
"Certainly [it] has elicited a reaction unlike any in a generation around the defense of workers' rights, to collectively bargain," said McCartin.
But McCartin said that the labor movement had lost strength compared to a generation ago, a story told in the raw numbers.
According to a January report from the Bureau of Labor Statistics, union membership in 2010 was 11.9 percent of the American work force, down from 12.3 percent in 2009. The number of employees belonging to a union declined by 612,000, to 14.7 million.
Nearly 30 years ago, that percentage was 20.1 percent, and there were 17.7 million union workers. In the mid-20th century, 35 percent of the work force was in a union.
But Daniel DiSalvo, a political science professor at City College of New York who studies the U.S. labor movement, said the distinction between public- and private-sector unions is important when looking at the numbers.
While private-sector union membership has declined steadily, public union membership has remained strong. More than one-third of government workers (about 7.6 million of them) belong to a union, compared with 7 percent of private-sector workers (or 7.1 million), according to the Bureau of Labor Statistics.
"Even with declining membership, the rise and increase in political power of public sector unions has helped stabilize ... the labor movement," DiSalvo said. "The heart and soul right now of the labor movement is public employees."
DiSalvo and McCartin believe that the political strength of the labor movement has not declined, despite the drop in overall union membership.
"Unions have done better at mobilizing their members and getting them out to vote, and so unions have retained a good deal of political influence even as their membership numbers have gone down," McCartin said.
"Organized labor relies on people power -- its members getting out door to door, talking to each other and other working Americans, working phone banks and turning out the vote. It's the organizational capacity of a Get Out the Vote effort that has been labor's key tool."
DiSalvo drew a further distinction:
"Public employee unions are much more political for reasons that are obvious," he said. "They try to elect their own boss, which is not something that private sector unions could ever dream of," he said. "The United Auto Workers are not selecting the CEO of General Motors."