The tally includes about 68,000 new voters in Ohio -- one of the most contested battleground states this year -- and thousands of other union-friendly voters in swing states like Colorado and Nevada.

"That's an amazing number," said Paul Beck, a political science professor at Ohio State University. "In an era of declining union membership, one wouldn't think there would be many new targets out there."

Obama defeated Republican John McCain by a little more than 200,000 votes in Ohio in 2008 out of about 5 million votes cast in the state.

In West Virginia, the union registered more than 8,600 voters from union households, according to a union official. The push increased the percentage of West Virginia union household members registered to vote from 58 percent to 66 percent, according to the union.

Voters from union households have traditionally favored Democratic candidates. That trend is expected to continue this year in light of high-profile efforts by Republican leaders to weaken collective bargaining rights in Ohio, Wisconsin, Indiana and other states.

In 2008, exit polls showed 59 percent of voters who lived in union households backed Obama, while 39 percent supported McCain. Union household voters split similarly in the previous two presidential elections.

"This is the first time we've made this big an effort to increase registration," said Mike Podhorzer, AFL-CIO political director. "We're really proud that more union members are going to be engaged. Whoever they vote for, the fact is we're increasing civic participation."

Podhorzer said the plan began in March 2011, when the labor federation began matching lists of union household members with voter registration files from every state. It then identified about 2.3 million people living in households of active and retired union members who were not registered to vote.

Union leaders hoped to register at least 20 percent of that number. That would raise the estimated overall union household registration from 70 percent to 75 percent of eligible voters.

The task was easier in states like Ohio, where union density is highest. In Pennsylvania, for example, Podhorzer said the AFL-CIO registered 57,000 new voters from union households. But the federation also made gains in other swing states, registering 13,500 in Colorado, 10,000 in Nevada and 6,700 in Virginia.

Unions have been trying to maintain their relevance as major political players amid years of steady declines in membership. The voter registration drive could help labor leaders maximize their impact with the numbers they have.

Podhorzer said the project had already met the 75 percent goal as of early August, and he hopes to exceed it in the next four weeks. In the general population, about 65 percent of people 18 and older are registered to vote, according to Census Bureau figures.

Most of the registration work is being done by the federation's 56 affiliated unions, which represent about 9 million workers with collective bargaining agreements.

Unions expect to spend hundreds of millions of dollars to help Obama and other mostly Democratic candidates for state and federal office win election. The AFL-CIO is devoting most of its attention to six battleground states: Florida, Michigan, Nevada, Ohio, Pennsylvania and Wisconsin.

"I think there is an enthusiasm among these voters, a feeling that unions are embattled these days," said Beck, the political science professor. "Given what's happened to unions since 2010, they may be more energized than normal to vote for a Democratic candidate."