His rags-to-riches immigrant journey and good business sense crowned Juvenal Chavez the king of Latino supermarkets in the Bay Area, but now the CEO is fighting to save the reputation of his 21-store Mi Pueblo Foods grocery chain.

Mi Pueblo stunned some of its more than 3,000 employees last month when it told them it had joined E-Verify, a Department of Homeland Security program that screens the immigration status of new hires.

Now, with union activists accusing Chavez of betraying his own undocumented immigrant roots and threatening a consumer boycott if he doesn't pull out of E-Verify by October, the entrepreneur is fighting back in a war of words against the union and political opposition.

A protest outside the chain's San Jose headquarters on Thursday was "part of an ongoing campaign against Mi Pueblo (to) damage our good name," said spokeswoman Perla Rodriguez, who accused labor unions of an underhanded campaign to distort the company's record of advocacy for the Bay Area's Latino community.

Lauded by city leaders around the Bay Area for buying up vacant or rundown big-box supermarkets and transforming them into colorful, festive Latin American food markets, Chavez is now confronting one of his biggest public-relations challenges since he founded the company in 1991 on San Jose's Eastside.

Among Mi Pueblo's most prominent critics is Santa Clara County Supervisor David Cortese, who claimed in December that armed security guards escorted him from a San Jose store when he paid a visit after hearing complaints about work conditions. The company had said the visit by Cortese, a likely 2014 candidate for mayor of San Jose, was a union-organized "media stunt."

Now, the E-Verify controversy is fueling the ongoing disputes. Labor organizers trying to unionize Latino and Asian ethnic markets across the state are attacking Chavez as a hypocrite, citing past media reports in which he revealed he came to the United States illegally from Mexico as a young man in the 1980s.

"He comes here undocumented and now he's going after undocumented workers," said Mike Henneberry of the United Food and Commercial Workers Local 5. "I think that's a little hypocritical. If it's not hypocritical, it's a little ironic."

Rodriguez countered that Chavez is a longtime U.S. citizen and a community advocate who supports fixing the "broken" immigration system and has funded scholarships for undocumented students. She said she didn't know how he arrived to the country. That question, she said, is "very personal and it is not pertinent to operation of the company." Chavez declined repeated requests for comment.

After arriving to the United States in the 1980s and working as a janitor at Stanford University, Juvenal Chavez worked with his brother David Chavez to found Redwood City's Chavez Meat Market in 1984, expanded into Menlo Park in 1993 and now runs the 8-store Chavez Supermarket chain.

Soon however, Juvenal Chavez's own company began to eclipse his brother's business, and is now an empire that stretches from Vallejo to Salinas and the Central Valley. It has been fighting for several years with a union that accuses it of mistreating workers.

For now, many of the popular chain's loyal customers remain unaware of the controversy.

"That's kind of unexpected for a store like this," said Jonathan Rodriguez, 18, as he helped his grandmother on Thursday stuff grocery bags into her trunk at the Mi Pueblo store in central Hayward. "I don't think that's right. They are a Mexican food center and they should be helping their community."

Another regular customer, Rafael Nunez, says the "law is the law" and Mi Pueblo is doing what it needs to do.

"In any country you go to, the law says you need papers to work," said Nunez as he went searching for a fresh mango with his young grandson.

Mi Pueblo signed up for E-Verify on Aug. 14, joining more than 30,400 California employers and 109,205 work sites across the state that belong to the expanding work-verification network, according to Sharon Rummery, spokeswoman for U.S. Citizenship and Immigration Services.

The San Jose-based grocer is also among a growing number of supermarkets in the program.

Pleasanton-based Safeway uses E-Verify, but only in Arizona, where the state requires its use. Modesto-based Save Mart, which includes the Lucky store brand, also uses E-Verify to screen workers, as do Berkeley-based Grocery Outlet and Berkeley Bowl and several Latino grocery chains such as Vallarta Supermakets and El Super, both headquartered in Los Angeles County, according to the federal government's list of all E-Verify employers.

Mi Pueblo joined upon the federal government's recommendation, said Rodriguez, who said it was a tough decision for company executives to make.

"This is something many Hispanic grocery stores" have to deal with, she said.