CONCORD — A crew of federal officials wandering into a day labor hiring zone used to mean one thing: time to leave.

Not the case Thursday morning on Monument Boulevard. Armed with coffee, not handcuffs, investigators from the U.S. Department of Labor chatted warmly with Latino immigrant workers about how to find jobs without being exploited.

"We're the feds, but the good ones," said Paul Ramirez, speaking in Spanish inside the Michael Chavez Center, a gathering spot for day laborers. "We're here to help workers."

The unprecedented visit was part of a campaign to bring long-established workplace protections to the nation's most vulnerable and underpaid workers, including those who have no legal right to be living in the United States.

"Documented or not, the law is: If you work certain hours, you are owed certain money," Ramirez told the small crowd. Met at first with apprehension, the Brentwood native captivated his audience of men from Mexico and Central America as he told of tending tomatoes, onions, asparagus and cucumbers as a young California field hand. Now an enforcer of workplace rules, he advised what to do when contractors skirt the law.

"We already knew some of these things, but now we feel more comfortable, more support," said laborer Gilberto Villanueva, who came to the East Bay eight years ago from southern Mexico. "It's good that they came."

There was nothing new about the standards Ramirez mentioned: minimum wage, overtime, sick leave. But none of the workers had heard this before from a federal agent. "We've always been very active in the community, but now we're becoming more vocal, more transparent," said Susana Rincon, Bay Area director of the labor agency's wage and hour division. "Other than that, the message is the same."

Ramirez made the same speech recently to workers who gather outside a Home Depot in Pittsburg. And it's not only a message for day laborers; it was delivered Thursday at the Chinese Newcomers Service Center in San Francisco.

The awareness campaign, called "We Can Help," is being led by Secretary of Labor Hilda Solis, a former Southern California congresswoman who joined the Obama administration early last year.

Solis inaugurated the campaign Thursday in Chicago with a speech at the Jane Addams Hull-House Museum, a 19th century landmark of labor reform and social welfare movements. She said she has added more than 250 field investigators, bringing the total to nearly 1,000 nationwide, about the same as at the beginning of the Bush administration.

The investigators have no jurisdiction over homeowners who hire day laborers for temporary landscaping, moving and domestic work, but they do have authority over contractors who make at least a half-million dollars, Rincon said. If workers with a problem call investigators, usually the issues are resolved by phone within 24 hours, Rincon said. In rare cases, the investigators will visit work sites or take employers to court.

Day laborers "know laws are out there to protect them, but they don't always believe it, or know that it can be enforced," said Mike Van Hofwegen, director of the Concord work center. Van Hofwegen was as surprised as his clients when the labor department team called to say they wanted to visit.

"This is the first time we've had this kind of connection," he said. "Someone asked me, 'Is this an April Fools' thing?' "

Such a discussion between federal employees and workers who are, for the most part, illegal immigrants, is likely to engender controversy, but could also do everyone some good, he argued.

"It helps U.S. citizens because they're not being undermined by abusive labor practices in the community, because things are more competitive," Van Hofwegen said.