Green, a 26-year-old Detroit janitor, normally would have discarded the flier, but he had just learned he was about to become a father again. He was drawn to the union message of a better living, job security, benefits and health insurance.

Green attended the rally, joined the union and set out to evangelize, signing up new members for the budding Service Employees International Union Local 3.

Unions must convince a new generation of workers that unions can deliver tangible benefits, experts say. They have to reach out to new groups - young workers, students, immigrants, day laborers and service-sector employees.

"That is absolutely the future and the vitality of the labor movement," said Harley Shaiken, a labor relations professor at the University of California Berkeley.

At the end of 2005, union members made up 12.5 percent of the U.S. work force and 20.5 percent of the Michigan work force, about half the level of 30 years ago, according to recently released Census Bureau data and historical data compiled by UnionStats.com.

Companies increasingly are cutting benefits. The percentage of workers covered by employment-based health insurance has fallen for five straight years, from 63.6 percent in 2000 to 59.5 percent in 2005, according to census data.

"Workers with union representation have much more of a voice in what's going on than without union representation," said Gary Chaison, professor of management at Clark University in Worcester, Mass. "Employment is very insecure in the United States without unionization."

The UAW, one of the most visible unions in the United States, is an example of what's happening in the manufacturing sector. With 550,000 members, the UAW is about one-third the size it was in the late 1970s and figures to lose more members in the next few years.

Ford Motor Co. and General Motors Corp. are cutting about 30,000 hourly workers each. Dozens of Michigan-based auto suppliers, including Delphi Corp., Collins & Aikman Corp. and Tower Automotive Inc. are working their way through bankruptcy court and looking to cut their hourly work force.

"Only a small proportion of the work force might find unions to be relevant to their needs," Chaison said. "There's a need to broaden the scope of what can be offered."

While manufacturing unions are taking a hit, a bright spot for union growth can be found in the service sector, said Ruth Milkman, director of the Institute for Industrial Relations at the University of California, Los Angeles.

From 2000 to 2005, the Service Employees International Union, which represents workers in fields such as maintenance, health care support and food preparation, increased membership 10 percent to 1.5 million, according to filings with the U.S. Department of Labor.

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