For most of their history, labor unions opposed attempts at loosening immigration laws and often threw their weight behind restrictionist measures. During the most recent overhaul effort in 2007, a schism among unions cracked an otherwise willing liberal coalition and helped defeat the reform bill. But now, in the wake of Arizona's strict and highly controversial new immigration law, labor has united to support immigration reform with unprecedented vigor.

AFL-CIO President Richard Trumka. Critiquing the Arizona law, he said, "All of us should fear such a system. In the end, don't all of us who aren't Native Americans look like the immigrants and children of immigrants that we are?" (EPA/ZUMApress.com) Richard Trumka, president of the 11.5-million-member AFL-CIO, gave a pivotal speech on June 18 at the City Club of Cleveland that crystallized labor's shift in outlook. Trumka, the nation's most powerful labor voice, made a moral and economic case for reform and pledged to "face head-on our own contradictions, hypocrisy and history on immigration." AFL-CIO has joined forces with the 2.2-million-strong Service Employees International Union and the United Food and Commercial Workers International Union to pour resources into the fight, and the three have written a joint letter to Congress detailing labor's "unified position and unfailing commitment" to sweeping reform.

Labor leaders have come to view an immigration overhaul as an opportunity rather than a threat to their interests. A large population of unlawful immigrants undercuts both the working class and the influence of unions, while legalized immigrants could be tapped to expand union membership. Likewise, joining forces with the pro-reform and growing Hispanic community can help secure the movement's future.

Labor unions' share of the U.S. workforce has declined steadily since the 1950s, when the figure peaked at roughly one-third. Last year it was 12.3 percent, according to the Bureau of Labor Statistics.

"Immigrant workers are the growth sector in today's labor movement, so they're a big part of its future," said Kate Bronfenbrenner, director of labor education research at Cornell University.

Mark Krikorian, executive director of the restrictionist, "low-immigration" Center for Immigration Studies, put it more bluntly. "Unions obviously see immigration as their only chance at future growth," he said, "since American workers have pretty much given up on them."

A January report by the liberal Center for American Progress and Immigration Policy Center noted that a large population of unauthorized immigrants - 10 to 12 million, per most estimates - depresses wages for low-skilled jobs. Unscrupulous employers can hire and underpay unlawful workers, who have no ability to unionize or push back politically. In other words, the larger the undocumented population, the smaller the clout of organized labor.

Legalizing unlawful immigrants and ensuring the rights of all workers, the CAP and IPC study concluded, would "help American workers" by "rais[ing] the ‘wage floor' for the entire U.S. economy." Newly naturalized workers could also give unions a boost, particularly if they view them as allies early on.

"We want a strong legalization program, and we want to legalize as many workers as fast as possible," said Ana Avendaño, director of immigration at AFL-CIO, adding that the AFL-CIO supports the creation of an "independent commission" to structure requirements for future immigration inflows based on the needs of the economy.

While these undercurrents have been brewing for years, the newly galvanizing force for labor is the Arizona crackdown on illegal immigration, which requires law enforcement officials to probe the residency status of suspect individuals during lawful encounters.

"Right now, the big fire that's pushing the labor movement is what's happening in Arizona," said Bronfenbrenner. "It's hurting workers all over the country." Trumka forcefully criticized the law in his Cleveland speech as part of "a hate campaign" against "working people," one that's designed to "make anyone who might look like an immigrant live in fear of the police."

Civil rights groups say the law will disproportionately target Latinos - the fastest-growing U.S. demographic, and one that strongly backs an immigration overhaul. Unions are already leveraging their pro-reform stance to reach out to Hispanics - an effort that, if successful, could substantially boost their membership prospects in the long run.

The battle over this issue is ongoing, as five states are currently developing similar laws to Arizona's, and 17 more have shown interest in it, according to the think tank NDN. "We're very concerned that Arizona is going to become the model for the United States," Avendaño said.

A sticking point for labor continues to be the expansion of the current guest worker program, the primary reason for AFL-CIO's opposition in 2007. This business-backed clause comprises non-immigrant visas such as the H-1B, which grants skilled foreigners the temporary right to live and work in the United States. But because these short-term workers have limited job flexibility and are essentially unable to unionize, the provision has been a roadblock to labor's goals of having a politically active workforce and protecting low-skilled domestic talent.

Trumka, who calls recipients of these visas "vulnerable, indentured workers," reiterated his union's opposition to them in Cleveland. "We will not support the return to outdated guest worker programs that give immigrants no security, no future here in the United States, no rights and no hope of being part of the American Dream," he said, demanding that all workers be "able to assert their legal rights, including the right to organize, without fear of retaliation."

But Avendaño declined to say whether AFL-CIO and other unions might again seek to kill reform over this provision. "It's really hard to picture how this will end up," she said, adding that labor "won't support reform that puts working people in a bad position." During the 2007 effort, dissenting progressives such as Sens. Sherrod Brown (D-Ohio), Byron Dorgan (D-N.D.) and Bernie Sanders (I-Vt) cited the bill's expansion of this program as a prime reason for joining all but 12 Republicans to narrowly defeat it. Labor unity on the next effort could play an important role in swinging the votes of liberals.

With the midterm elections approaching, Democrats appear to have put off immigration reform until next Congress, but have intensified support for it since the Arizona law's enactment. They released a broad template on April 29 - less than a week after the Arizona bill was signed into law - proposing to beef up border security, create a pathway to citizenship and overhaul the systems for employment- and family-based immigration. After helping Democrats pass health care reform, unions are poised to flex their muscle on this new priority.

To Krikorian, labor's embrace of immigration reform is part of a broader cultural shift. "The U.S. labor movement has changed and become more like European unions - post-patriotic, culturally leftist - and the change in immigration policy is just part of that change," he said.

For Trumka, however, the case for immigrant rights isn't just about workers, politics or the economy - it's also about the fabric of American society. Critiquing the Arizona law, he said, "All of us should fear such a system. In the end, don't all of us who aren't Native Americans look like the immigrants and children of immigrants that we are?"