The Laborers' Union, which represents 700,000 workers in the construction industry, has decided to leave the AFL-CIO, officials said.
The Laborers were already part of the Change to Win coalition, breakaway unions that have left the giant federation of more than 50 unions in an effort to forge a new direction for organized labor. But the Laborers had remained in the federation.
"We are leaving so that we can place our full efforts and focus on growth in order to help millions of construction workers improve their lives," said Richard Greer, a spokesman for the Laborers. The Laborers informed the AFL-CIO Monday that they are leaving as of June 1.
The Laborers, the Service Employees International Union, the Teamsters, the United Food and Commercial Workers, UNITE HERE, United Farm Workers and the Carpenters are part of the Change to Win coalition.
AFL-CIO officials had no immediate comment on the latest defection from their ranks.
The breakaway unions have complained that the AFL-CIO was putting too much emphasis on electoral politics and not enough on organizing more people to join the shrinking labor movement.
AFL-CIO leaders argue that organizing and politics are equally important in protecting the rights of working Americans. Despite their differences, the AFL-CIO and the Change to Win unions recently announced they would work together this year to coordinate political efforts.
The Laborers' International Union of North America has about 700,000 members in the U.S. and Canada, mostly in the construction industry. Those in the Laborers' union are in a wide variety of construction trades, and also work in demolition and cleaning up hazardous materials such as asbestos and lead.
A large share of the unions' newer members are recent immigrants, including many Hispanics.
Greer said construction workers have seen declines in wages, benefits and working conditions over the last decade.
"We want to change that," Greer said, "so construction workers are better rewarded for the hard, dirty and sometimes dangerous work they do."