NEW YORK (CNNMoney.com) -- As politicians grapple with the thorny immigration issue, unions are stepping into the debate on the side of illegal immigrant labor.

Last week, the AFL-CIO signed what it calls a "historic partnership agreement" with the National Day Laborer Organizing Network, an association of 40 worker centers nationwide.

Under the agreement local AFL-CIO unions will be allowed to establish formal ties with the local worker centers. The unions then work with and defend the NDLON centers as they seek decent labor standards and working conditions for their illegal workers.

The NDLON sprung up in 2000 as a collaborative effort between community-based organizations' worker centers that support day laborers - overwhelmingly poor, illegal immigrants from Latin America - by providing meeting spaces, staff to handle workplace violations, and access to healthcare, English classes and workers' rights education.

Under the agreement, the AFL-CIO will also combat anti-immigration legislation and pursue immigration reform with a "clear path" to citizenship.

By offering the advantages of organized labor, without actually unionizing the illegals, the AFL-CIO also hopes to raise the wage floor in the local labor markets and in turn take pressure off wages paid to local union members, too.

"In many ways this is unprecedented for the modern labor movement," said labor historian Joseph A. McCartin, of Georgetown University. "The AFL-CIO was for immigration enforcement in 1999."

McCartin says the labor movement must reinvent itself in this way if it wants to continue after years of declining influence.

Day laborers represent a sliver of all illegal workers in the United States. There are an estimated 117,000 day laborers in the U.S. economy, according to a 2006 National Day Labor Study. About half are employed by homeowners, while 43 percent work as construction contractors.

The AFL-CIO announced the agreement a year after seven dissident unions broke off from the organization over disagreements about recruitment strategies and funding priorities.

The dissident unions formed the Change to Win coalition.

"The AFL-CIO's alliance with NDLON can be seen as a response to the Change to Win split," McCartin explained. "The SEIU (of the Change to Win coalition) has made special efforts to organize immigrant workers."

A day after the AFL-CIO announcement, Laborers International, a construction trade member of Change to Win, went a step further than the AFL-CIO by announcing plans to begin organizing undocumented workers in the residential construction industry in California beginning in 2007.

"For us it's a matter of mission and relevance," said Richard Greer, spokesman for the Laborers International, who said it had been planning the move for some time.

"Our mission is to help construction laborers lead better lives...If the workforce is predominately immigrant, then we can't represent construction workers if we don't represent their needs," he said.

Greer notes undocumented workers are among the lowest paid and most mistreated in the industry.

McCartin of Georgetown sees historical parallels between where the labor movement is today and where it was in the beginning of the 20th century.

Both periods were marked by years of declining membership and a surge of immigrant labor entering the market, he said.

"Before WW I there was no restriction (on the number of) documented workers. Labor was welcomed and flooding into US."

In the 1920s, the unions grew by actively recruiting that labor, McCartin said.

Ana Avendaño, director of AFL-CIO Immigrant Worker Program, concurs.

"These workers are acting collectively to raise the minimum wage right now. They're acting like trade unionists at the turn of the last century."

Talk of aiding illegal immigrants, as the AFL-CIO will, or organizing them as Change-To-Win plans, immediately raises questions of a cultural backlash among existing union members.

"There are members, to be sure, who feel strongly that the union shouldn't welcome undocumented workers," Greer of Laborers International says.

But he points out that Laborers International has done internal polling on the subject and found that while some members will oppose the recruitment of undocumented workers, 70 percent think there should be a path to citizenship for them.

A sampling of unionists found similar responses.

"We agree with the basic gist of what the AFL-CIO is doing. The undocumented workers are bettering themselves," said Robert Hamner, IBEW union organizer in Birmingham, Ala. "The only problem I have is that we would certainly rather have legal immigrants."

Hamner is quick to point out, however, that the issue of undocumented workers extends beyond the labor market to matters of border control and national security.

Knowing who is on the construction site is another reason Greer gives for why the Laborers International will organize undocumented workers.

"Anecdotally, some in the building trades are upset," said Robert Shaw of the Harris County AFL-CIO Council in Houston. "But some non-union commercial contractors are upset because they can't compete with the low wages as they are."

Half of the day laborers surveyed in the National Day Labor Study report having wages withheld from them by unscrupulous contractors.

Their annual income hovers around $15,000 a year, according to the study.

Shaw, who works near a bus station in Houston, said he sees undocumented workers departing for Atlanta every day. From Atlanta they travel to cities throughout the eastern half of the U.S., he says.

He admits voters may not like the idea of unions organizing illegal workers but he says unions have to help day laborers to keep the wage floor up, which affects all workers in America.

"We're having to deal with the wage floor," Shaw said, which in Houston has plummeted over the years. "It worries me to death."

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