Union membership numbers in the U.S. are finally looking up.

The number of union members was 16.5 million in 1999, a net increase of 265,000 workers from the year before, reported the U.S. Department of Labor. It was the largest increase in union membership in more than 20 years.

In the building trades alone, union membership numbers increased by 131,000 from 1998 to 1999, the largest jump in decades. The IBEW alone accounted for 50,000 new members.

"Today's data indicate that our renewed emphasis on helping working people form unions is having an impact," said AFL-CIO President John Sweeney. "Our challenge for the future is to remain focused and to broaden our efforts. It's crucial for unions to continue to grow if working men and women are going to have a stronger voice in the issues that matter to them most."

Union membership had begun to reverse its steady decline in 1997-1998 - when the numbers were essentially stagnant - and now stands at 16.5 million members. Turning around the negative trend is such a daunting task because so many workers are lost every year to attrition. At least 600,000 workers joined unions in 1999, but with attrition, the net gain was 265,000. The overall percentage of workers who carried a union card in 1999, 13.9 percent, didn't change from 1998.

"Given the very powerful forces that labor continues to confront, it does represent an important step in the direction in which unions want to go," said University of California at Berkeley labor professor Harley Shaiken in the Wall Street Journal. "One would be cautiously optimistic looking at these numbers."

One particularly bright spot for union labor was a gain of 112,493 members working in the private sector, nearly double the size of the only other such annual increase in two decades. In the recent past, government jobs have been the stronghold of union labor. Now, labor's message is getting out to a variety of occupations. For example, 45,000 doctors joined unions in 1999 and 75,000 home health aid workers were unionized in California alone.

"The private sector growth is a clear sign that our efforts to think strategically and creatively are beginning to bear fruit,'' said Kirk Adams, the AFL-CIO's organizing director.

In 1999, government workers continued to have a substantially higher unionization rate (37.3 percent) than workers in the private sector (9.4 percent). The organized U.S. construction industry, with just over three million workers, enjoyed one of the highest unionization rates in the private sector, jumping from 17.8 percent to 19.1 percent.

Economist Ken Goldstein of the Conference Board, a business-sponsored study group in New York, advised labor not to declare victory yet.

"Unless they can start to organize the office, days like this are going to be few and far between," he said. "For all good news this is from their point of view, this is a quite limited and perhaps a quite temporary celebration."

Many labor unions are committing serious resources to make sure the increase in numbers isn't temporary. The labor community has doubled the resources spent on organizing in the last four years, and more unions are prioritizing organizing in their budgets. For example, the Operating Engineers committed $15 million to organizing, following AFSCME and the Steelworkers, who last year committed more than $40 million to help workers join unions.

Sweeney said there is more work to be done. "We're turning the corner, but we're not at our destination yet," Sweeney said. "Our challenge for the future is to remain focused and to broaden our efforts."