That April 10 nearly six years ago was one of Jaime Contreras’s defining moments.

People arrived on the Mall by the tens of thousands, waving American flags and chanting in Spanish, “Yes, we can!”

Contreras, 37, still vividly remembers the vigor of more than a quarter of a million people demanding immigration reform.

“I was proud. . . . The thing that made me the most nervous was [thinking], ‘Where do we go from here?’ ” Contreras said.

Contreras, who chairs the Capital Area District of 32BJ, an affiliate of the Service Employees International Union, has become one of Washington’s most active advocates for immigrant rights. At congressional and local government hearings, he has lobbied for the estimated 11 million undocumented immigrants in the country.

He is leading efforts this year in Maryland to win approval, in a referendum, of the state’s version of a Dream Act, which would grant in-state college tuition discounts to undocumented immigrants.

“He is sort of what the union leader of today needs to be,” said Eliseo Medina, SEIU’s international secretary-treasurer. “He sees his mission as being broader than just simply the workplace but really being able to help deal with the issues in the broader society where our members live — not just where they work.”

Contreras was 17, in high school and working nights as a cleaner at 1800 M Street when he started his career as a unionist in 1992.

He was one of a handful of part-time workers who spoke English and Spanish and quickly became the go-to person when someone needed help communicating with supervisors or co-workers. The workforce at the time was half Hispanic and half black, he said. They were paid about 10 cents above the $4.75 minimum wage and had no benefits, Contreras said.

“Somebody would call out sick, and the next day they wouldn’t have a job,” he said. “But what probably got me more upset at that age was when people were being . . . mistreated for no reason. They weren’t treated with dignity or respect.”

Contreras was energetic, unafraid of losing his job and “really interested in making things right,” said Valarie Long, a union organizer at the time and now executive vice president of SEIU.

After six months of training and organizing, Contreras led his co-workers on a two-day strike, which led to an agreement for salary increases, vacation time and sick days. He was soon working part time as a union organizer while attending Bell Multicultural High School in the District.

After high school, Contreras served three years in the Navy, then returned to the union to become the youngest Latino, at age 27, to hold a full-time elected position in an SEIU local. He also is the first Latino president of SEIU Maryland and DC State Council, a political arm of SEIU.

The local union membership has grown from about 7,000 in 2006 when Contreras was elected district chairman to more than 16,000. The majority are Hispanic immigrants.

“Their families are suffering because of the current broken immigration system, and that’s why this is personal for me,” said Contreras, who illegally immigrated to the United States from his native El Salvador in 1988.

Illegal immigrant

At age 13, Contreras crossed the U.S.-Mexican border with a younger brother and a couple dozen other Salvadoran immigrants, who each had paid about $3,000 to a smuggler.

“For us, it was an ad­ven­ture,” said Contreras, recalling the 24-day trip along Mexico’s mountains.

His father, Victor Contreras, an ambulance driver in El Salvador’s second-largest city of San Miguel, had arrived in the United States a few years earlier, fleeing a bloody civil war in the early 1980s. He had saved up to bring his six children to the District two at a time.

Once here, Jaime Contreras started to show an aptitude for activism.

“Jaime was my interpreter,” said Victor Contreras, recalling how the boy helped when his father organized tenants at a building on T Street NW.

His son remembers that the landlord would raise the rent and wouldn’t fix things when they broke.

“I had no idea I was being an activist. I was just helping my dad out,” said Contreras, who lives in College Park with his wife and two of his four children. He earned U.S. citizenship in 1996 after receiving political asylum.

Controversial figure

Widely admired in Washington’s immigrant community, Contreras has vocal critics.

“One of the surprising things for me is that he brings in all of these workers who cannot legally be employed to work as janitors and then complains . . . that they don’t earn enough,” said Greg Letiecq of the anti-illegal-immigration group Help Save Manassas. “And then he goes and does these outrageous protests to try to make sure they can earn a living.”

The mass rallies Contreras led in the area in the mid-2000s weakened chances for reform, Letiecq said.

“He got a bunch of people upset, and he didn’t get amnesty for his illegal aliens,” he said. “People like him have polluted the dialogue so badly.”

Del. Patrick L. McDonough (R-Baltimore County), who is leading opposition to the in-state tuition bill, said that any success Contreras has had is because of allies in Annapolis.

“He is talking to friendly people, to people who are advocates for illegal immigration. It is not like Contreras has to use his talent or some special power to convince them,” McDonough said.

But before Contreras, immigrant rallies in the Washington region were organized by groups from outside the capital area, said Gustavo Torres, executive director of CASA of Maryland. None had been as massive as the April 10, 2006, event, he said.

“He took the leadership to organize all of us. I remember he went one by one to different organizations,” said Torres, who believes it is going to take leadership from someone like Contreras to reignite the reform effort.

Since that rally, several states have enacted laws targeting illegal immigration, and the Obama administration has deported people at a record rate: an average of nearly 400,000 per year.

Contreras said he remains optimistic.

“My hope is that if we elect the right people . . . that we will be able to press forward as a community hard enough to get the immigration reform done so people are not being scapegoated and families are not separated and children left without parents and parents being deported,” he said.

“Hopefully, we can change that in the next couple of years.”