CHICAGO - Unions across the U.S. are reaching out to immigrants affected by President Obama's recent executive action, hoping to expand their dwindling ranks by recruiting millions of workers who entered the U.S. illegally.

Labor leaders say the president's action, which curbs deportation and gives work permits to about four million immigrants, will give new protection to workers who have been reluctant to join for fear of retaliation.

"I think we'll see very positive changes" because of the action, said Tom Balanoff, president of Service Employees International Union Local 1. "One of them, I hope, is that more workers will come forward and want to organize."

SEIU, whose more than two million members include janitors and maintenance workers, recently announced a website where immigrants could learn about the action. The AFL-CIO says it's training organizers to recruit eligible workers. And the United Food and Commercial Workers and other unions are planning workshops and partnering with community groups and churches to reach out to immigrants.

The efforts come even as Republicans and other opponents of Obama's action work to undo it, saying it will hurt American workers, and as some labor experts say they're skeptical immigrants will feel safe enough to unionize in large numbers.

Labor unions have struggled over the last decade to maintain their membership and political muscle. The ranks fell by more than 1.2 million between 2003 and 2013, when there were about 14.5 million members nationwide, according to the Bureau of Labor Statistics.

Business-friendly Republican governors have approved measures in recent years aimed at weakening labor, even in places such as Michigan that were once considered union strongholds.

Unions say they can help protect immigrants against abuses such as wage theft and discrimination. And even if the immigrants aren't citizens and cannot vote, they can help unions by paying dues and doing the heavy lifting needed around election time.

Republicans say the executive actions - which would affect people who have children and have been in the U.S. more than five years - will make it tougher for Americans already struggling to find good-paying jobs. They've pushed legislation to void the new protections.

"The president's action is a threat to every working person in this country - their jobs, wages, dreams, hopes, and futures," said Sen. Jeff Sessions (R., Ala.).

Felipe Diosdado, who came to the U.S. illegally in 1997, says undocumented people he knows are working for cash at small businesses that aren't unionized because they're afraid to apply at larger job sites that are more likely to verify a worker's immigration status.

And while he acknowledged that many immigrants were fearful because the protection was temporary and could be undone by a future president, he expected some to sign up.

Shannon Gleeson, an associate professor at Cornell University's School of Industrial and Labor Relations, said she expected the response to be "very place-specific," with people coming forward in places that have traditionally been considered immigrant-friendly, like Los Angeles, while being reluctant in places like Houston, where it's a struggle to find a unionized hotel.

"If I'm there, am I going to stick my neck out?" Gleeson said. "I don't know, maybe not."