(CNN) -- The AFL-CIO, the nation's largest labor organization, endorsed Sen. Barack Obama for president Thursday, calling him "a champion for working families."
"In so many ways, on jobs, health care, gas prices and the war in Iraq, our country is headed in the wrong direction," AFL-CIO President John Sweeney said in a statement.
"Barack Obama has proven from his days as an organizer, to his time in the Senate and his historic run for the presidency, that he's leading the fight to turn around America."
With an outreach of more than 13 million registered voters in 24 states, the AFL-CIO aims to send volunteers to the homes of 300,000 union voters.
The federation of 56 labor unions collectively is expected to spend more than $200 million in the 2008 presidential, Senate and House races.
"We'll work our hearts out for Barack Obama," said Gerald McEntee, president of the American Federation of State, County and Municipal Employees and the AFL-CIO's political committee chair.
"Our program is going to be worker to worker and neighbor to neighbor. We're ready to mobilize. We're ready to rock and roll. This country and our people are ready for change."
The AFL-CIO has been running an active campaign against Sen. John McCain, the presumptive Republican nominee, since March, aimed at defining his stances on jobs, trade and health care among union members.
AFL-CIO volunteers have knocked on 60,000 doors and distributed 1.5 million fliers critical of McCain's economic record, according to the federation.
The endorsement is expected to help rally support around the presumptive Democratic nominee in the critical swing states of Ohio, Pennsylvania, Michigan, Wisconsin and Minnesota, where union members make up between 25 percent and 35 percent of total voters, according to the group.
The International Brotherhood of Electrical Workers on Thursday also joined in organized labor's endorsement of Obama's candidacy.
"The issues are clear. We as a people face difficult choices on health care, energy policy and building jobs and opportunity in a world increasingly bound by economic and environmental issues," said Edwin Hill, the union's president. "Barack Obama offers positive leadership to navigate our way into the future instead of continuing the failures of the past."
These endorsements come as a poll released Thursday shows Obama leading McCain in four critical battleground states.
A Quinnipiac University/Wall Street Journal/Washingtonpost.com survey put Obama up significantly over McCain in Minnesota, 54 percent to 37 percent, and Wisconsin, 52 percent to 39 percent. The Democrat's lead appears smaller in Colorado, 49 percent to 44 percent, and Michigan, 48 percent to 42 percent, according to the poll.
The poll surveyed between 1,300 and 1,600 likely voters from June 17 through Tuesday, with a margin of error of plus or minus 2.5 percentage points in Minnesota and Wisconsin, 2.6 percent percentage points in Michigan and 2.7 percentage points in Colorado.
On Wednesday, Obama campaign manager David Plouffe sought to explain the strategy for reaching the 270 electoral votes needed to win the presidency.
The campaign is counting on winning the 20 states that Sen. John Kerry carried in 2004, looking to add Iowa and then setting its sights on others.
Plouffe called Michigan one of the most competitive states, which he attributes to Obama not campaigning or running ads in the primary there.
The latest CNN national "poll of polls" also has Obama up 47 percent to 40 percent over McCain among registered voters nationwide. The poll of polls does not have a sampling error.
It consists of six surveys: Los Angeles Times/Bloomberg (June 19-23), Gallup tracking (June 23-25), Franklin & Marshall (June 16-22), Newsweek (June 18-19), USA Today/Gallup (June 15-19) and Fox News/Opinion Dynamics (June 17-18).
On the campaign trail Thursday, McCain was slated to meet with conservative leaders in Cincinnati, Ohio
CNN's Ed Hornick, Alexander Marquardt and Emily Sherman contributed to this report.