At a recent Workers Defense Project meeting — they are held every Tuesday night — the atmosphere was part pep rally, part educational session, part social hour. After a dinner of tacos, rice and beans, about 60 workers plotted strategy for a demonstration against the developer of a 1,000-room Marriott hotel. A skit mocking the developer drew raucous laughter. The energy and sense of solidarity were reminiscent of what America’s labor unions had many decades ago, before they started to stumble and stagnate.

Worker centers, which are among the most vigorous champions of overhauling immigration laws, coalesce around issues or industries. For example, there is Domestic Workers United, which persuaded New York and Hawaii to enact a bill of rights for housekeepers and nannies, and the Coalition of Immokalee Workers, which has gotten most Florida tomato growers to adopt a workers’ code of conduct and to increase pay by at least 20 percent. Young Workers United played an important role in persuading the San Francisco City Council to enact a paid-sick-days law and a minimum wage of $10.55 an hour. With labor unions losing members and influence, these centers are increasingly seen as an important alternative form of workplace advocacy, although no one expects them to be nearly as effective as unions in winning raises, pensions or paid vacations.

“Worker centers are filling a void by reaching out to a work force that is particularly hard to reach out to,” said Victor Narro, a specialist on immigrant workers at the University of California, Los Angeles.

Jefferson Cowie, a labor historian at Cornell, said: “Worker centers are part of the broad scramble of how to improve things for workers outside the traditional union/collective bargaining context. They’ve become little laboratories of experimentation.”

As worker centers go, the Workers Defense Project in Austin has racked up an unusual number of successes. It has won more than $1 million in back pay over the last decade on behalf of workers alleging violations of minimum wage and overtime laws. A report it wrote on safety problems spurred the Occupational Safety and Health Administration to investigate 900 construction sites in Texas — leading to nearly $2 million in fines.

And, despite a liberal image, the group made common cause with law-abiding contractors to persuade the state’s Republican-dominated legislature to approve a law that made wage theft — an employer’s deliberate failure to pay wages due — a criminal offense. The Workers Defense Project has just 18 employees, and its executive director, Ms. Tzintzún, 31, earns just $43,000 a year. But it managed to bring mighty Apple to the negotiating table. The group extracted a promise that construction workers on Apple’s new Austin office complex would receive at least $12 an hour, not the more commonly paid $10 — as well as workers’ compensation coverage.