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WASHINGTON, D.C. -- Tens of thousands of immigrants and their supporters are scheduled to rally outside the U.S. Capitol, and across the country, as lawmakers inside prepare to unveil the biggest immigration bill in a generation.

There is also a demonstration outside the capitol in downtown Atlanta.

PHOTOS | Immigration rally outside Atlanta Capitol

The demonstration in D.C., dubbed the Rally for Citizenship, will feature speeches from immigration rights advocates, labor leaders, faith organizations and members of Congress working on immigration legislation. NAACP President Benjamin Jealous will deliver the keynote address.

The rally will coincide with marches, campaign-style door-knocking events and candlelight vigils in cities from Los Angeles to Orlando to Portland, Maine.

Immigration bills have been filed and killed repeatedly since the last major bill, allowing up to 3 million illegal immigrants to become U.S. citizens, became law in 1986. But organizers of Wednesday's rally say the political stars are finally aligned for another one.

"Every time you turn around, there's growing momentum for making this happen," said Mary Kay Henry, president of the Service Employees International Union, one of the groups that organzied the Washington rally. "They're voting, they're marching, they're dealing with their legislators ... to get their government to fix their broken immigration system."

The 2012 elections lit the fire, as Republicans struggled to garner Hispanic votes. That led longtime supporters of an immigration deal, such as Sen. John McCain, R-Ariz., and newcomers to the national stage, such as Sen. Marco Rubio, R-Fla., to call on the GOP to better serve the fast-growing electorate by exploring a broad immigration deal.

Now, bipartisan groups in the House and Senate are putting the finishing touches on their versions of immigration bills that would grant a pathway to citizenship for the nation's 11 million undocumented immigrants, tighten border security, require U.S. business owners to check the immigration status of new employees, and significantly alter the way the country distributes visas.

While sharp disagreements remain over the details of the proposals, President Obama has also supported a sweeping bill and has told Congress he would file his own bill if lawmakers don't act soon.

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