Figures released by the Bureau of Labor Statistics yesterday showed that union membership increased by 311,000 in 2007, ending a prolonged period of decline.

Unions were quick to hail the increase.

"Today's numbers show working people are pushing to form and join unions in order to improve their lives, despite record levels of resistance from employers," John Sweeney, the president of the AFL-CIO said. "They know that a union card is the single best ticket into the middle class, especially in today's economy."

In all, according to the Department of Labor, there were 15.7 million union members in 2007 who made up 12.1 percent of the economy's wage and salary workers.

The bureau found that half of all union members lived in just six states: California, 2.5 million; New York, 2.1 million; Illinois, 0.8 million; Michigan, 0.8 million; Pennsylvania, 0.8 million; and New Jersey, 0.7 million. Overall, those same six states counted for one-third of all the wage and salary jobs in the country.

The four states that had union membership rates above 20 percent were New York (25.2 percent); Alaska (23.8 percent); Hawaii (23.4 percent); and Washington (20.2 percent). In Pennsylvania the percentage of unionized workers was 16.6 percent.

The workers in unions also made more money than non-unionized workers, according to the bureau's statistics. In 2007, full-time wage and salary workers who were represented by unions had median weekly earnings of $863, while the nonunionized workers made $663.

Still, at 12.1 percent, the percentage of union workers nationally was up from only 12 percent in 2006 and significantly lower than it was in 1983, the first year for which comparable data is available from the bureau. In 1983, 20.1 percent of the workers were in unions.

But union leaders viewed the increase as a reason to celebrate.

"Our unions have been working hard over the last 10 years to build their strategic capacity to help workers join unions, even in this hostile legal environment where workers' right to organize has been all but eliminated," Mr. Sweeney said.

He said there have been significant organizing victories in the last year, with 40,000 child care workers in Michigan and 50,000 child care workers in New York joining unions. Other organizing victories included 40,000 communications workers, with 20,000 of them at AT&T Wireless; 6,000 casino workers in Connecticut and New Jersey; and 3,000 members of the administrative staff at Rutgers University in New Jersey.