The WDP, in particular, wins praise from the Michael Cunningham, executive director of the Texas Building and Construction Trades Council. "They expose unscrupulous contractors … and they reach out to workers who really had no advocate," says Cunningham, adding that unions, worker centers and well-meaning contractors have a common interest in maintaining safe jobsites and a reasonably well-paid workforce.

"We work on a lot of projects [in which] there are both union and non-union workers," he says. "Our members— with all the safety training they get—can be the safest guys on a job, but they can get killed if a non-union guy with no training makes a mistake. If [worker centers] provide safety training, that benefits everyone."

Some business advocates, however, suggest that worker centers are, in fact, acting much as labor unions do and should be subject to the same requirements.

Rep. Phil Roe (R-Tenn.) and chairman of the House of Representatives' subcommittee on health, employment, labor and pensions, says, "We should welcome any effort to improve the lives of America's workers, especially those struggling to make ends meet in this sluggish economy."

Roe adds, "However, those efforts have to abide by the law. If an organization meets the test of a labor organization as defined by federal law, then it has a responsibility to provide workers the transparency and accountability they deserve and the law guarantees."

In July, Roe and Rep. John Kline (R-Minn.), chairman of the House Committee on Education and the Workforce, wrote a letter to U.S. Dept. of Labor Secretary Thomas Perez, asserting that "the line between so-called 'workers centers' and labor organizations has blurred" and asking Perez for a formal determination on whether worker centers should be required to make the same regulatory filings as unions.

Worker centers typically describe themselves as charitable organizations focused on social and economic justice issues. Their leaders acknowledge, however, that they share many of the same goals as organized labor.

For example, Cuevas says the Los Angeles Black Worker Center's concerns regarding safety and fair pay align perfectly with the unions' concerns and that the center hopes the workers it trains will eventually find themselves in apprenticeship programs and as full union members.