Leslie Silverstein’s favorite day as a lawyer didn’t take place in a courtroom. It came at an arrival gate at O’Hare International Airport in Chicago, where a woman she represents in a pro bono asylum case was reuniting with her four young children.

“She hadn’t seen her kids for 2½ years,” Silverstein said. “It was like out of a movie.”

Silverstein, who has a solo practice in Portland, represents the woman from Burundi, seeking to have her permanently admitted to the United States after she fled the East African nation in 2010 following death threats from government officials.

As a result of Silverstein’s legal work, the woman’s children, whom she’d left with relatives when she escaped Burundi, had received permission to join their mother in the U.S. That emotional day at the airport in December 2012 was the first time she had seen them since fleeing.

The American Bar Association is recognizing Silverstein for that work and her other extensive pro bono, or unpaid, work for victims of domestic violence as one of five recipients of its prestigious Pro Bono Publico Award for 2015.

Silverstein, 51, will be honored Aug. 1 at the bar association’s annual pro bono awards banquet in Chicago. She will be attending with her entire extended family.

The national award surprised Silverstein, who learned about it in a phone call from the bar association. The people who nominated her never told her they’d done so, she said.

“I’m not saying I’m not worthy, but there are plenty of pro bono lawyers,” she said in an interview last week at her Newbury Street office.

But for those who nominated Silverstein, no other Maine lawyer does as much pro bono work in critically needed areas as Silverstein.

Juliet Holmes-Smith, director of the Maine Volunteer Lawyers Project, said Silverstein volunteers about 40 Fridays each year to take pro bono cases at the Cumberland County Courthouse in Portland during the court’s weekly docket for protection-from-abuse cases.

Silverstein makes a living entirely from representing clients in Social Security disability cases. Her work in asylum cases and from the protection-from-abuse cases is unpaid.

Both Holmes-Smith, who is a lawyer, and attorney Jennifer Archer, who is president of the board of Maine’s Immigrant Legal Advocacy Project, wrote letters to the bar association nominating Silverstein for the award. They decided to nominate her after both organizations separately honored Silverstein with their 2014 annual awards.

“It’s a big deal,” Holmes-Smith said of the ABA’s pro bono award. “She certainly seemed to fit the criteria they were looking for in a private attorney who was going above and beyond.”

Holmes-Smith said there are only about 30 lawyers on the pro bono panel who take the Friday protection-from-abuse cases. Those who can usually volunteer about six to eight times a year. But Silverstein, who first joined the panel in 2007, signs up for every week she can.

“It’s really clear to me when I look at the schedule that without Leslie there would be given weeks when we don’t have an attorney,” Holmes-Smith said. “She’s really the backbone of that program.”

On Fridays, the court sometimes calls as many as 20 protection-from-abuse cases. Some of those who can’t afford their own attorneys reach out in advance to Pine Tree Legal Assistance, which has a paid staff member for protection-from-abuse cases. But more than half of the people arrive without legal representation. Family Crisis Services refers many of those cases to whichever pro bono attorney is there that day, Holmes-Smith said.

The bar association would not say specifically why Silverstein was selected for the award, opting to issue a statement from its president about all five recipients.

“Offering pro bono legal representation to the most vulnerable in our society represents the best of our profession,” ABA President William C. Hubbard said in the written statement. “The recipients of the 2015 ABA Pro Bono Publico Awards inspire all of us to apply our skills as lawyers to serve others and to advance the cause of justice.”

Silverstein is the only recipient who has a solo practice. The other recipients are the Baylor University School of Law in Texas; attorney Daniel Brown, who works at a large firm in New York; Jones Day, an international law firm with headquarters in Boston; and the entire legal department at United Airlines.

“You don’t do (the pro bono cases) for an award. It’s a lovely surprise. That’s the best way I can put it,” Silverstein said.

Silverstein is a native of Long Island in New York, and moved to Maine in 1988 on a whim. She had made a close friend from Maine while attending law school at Tulane University in New Orleans, and followed that friend back to Maine after graduation to start her legal career. She has operated her own firm since 2001.

Silverstein started taking political asylum cases for the Immigrant Legal Advocacy Project in 2011, and would do that work full time if she could. The cases are very labor intensive, sometimes involving hundreds of hours of work.

Her first political asylum case was for the woman from Burundi. Silverstein declined to name her because the case is ongoing and family members in Burundi could face repercussions.

The woman had to flee Burundi in 2010 as result of her work as a rape counselor. She was an advocate for a 16-year-old girl who had been sexually assaulted by a man with a high-profile job and was coordinating her advocacy with a nurse who had treated the victim, Silverstein said.

First the nurse was murdered for speaking out, then Silverstein’s client began receiving death threats and went into hiding. She eventually decided to flee to America, leaving her husband and four children behind. When her husband began receiving death threats too, he followed his wife here, leaving the children with a sister, Silverstein said.

Silverstein estimates that she has worked more than 1,000 hours on the woman’s case, knowing that if the woman is sent back to Burundi she will be killed.

“You can’t lose. It’s basically a death penalty case,” Silverstein said.

Although the stakes are high and there is no pay, Silverstein said her pro bono work is hugely rewarding.

“I wish more lawyers would do it,” she said. “It could be an hour of your time, and it could change people’s lives.”