Five-month-old Chari Nguyen banged on the thick plexiglass window and cried. On the other end, her father, Dy, opened his arms and tried to calm her, repeating “Come to daddy” and “Daddy loves you”.

The 31-year-old father pressed his hands to the visitation room window at Stewart detention center, in a remote part of Georgia, getting as close as he could to his baby, who could barely hear his voice.

“She wants him to hold her, and all they can do is touch each other through the glass,” recalled Tammy Nguyen, Chari’s mother, who drove three hours that day in November to visit her incarcerated husband. “I keep trying to put Chari’s hand to where his hand was so he could feel connected to her.”

Four months later, Dy remains jailed with no end in sight. He is one of thousands of Vietnamese Americans now at risk of deportation as Donald Trump’s administration aggressively targets immigrant communities that had previously been protected.

Asian Americans Advancing Justice, a group representing Dy in court, has filed a class-action lawsuit against the US government challenging the continuing detention of Vietnamese refugees who fled war, violence, communist “re-education camps” and other forms of political persecution and are now threatened with removal to a country many of them barely know.

In March 2017, Immigration and Customs Enforcement (Ice) reversed a longstanding practice and began subjecting Vietnamese refugees to lengthy periods of detention under the threat of deportation, despite an agreement between the US and Vietnam that shields this population, the suit said.

“The change in policy has been so abrupt and has really pulled the rug out from under a lot of these communities,” said Phi Nguyen, litigation director at Advancing Justice-Atlanta. “These are people who really left everything behind, really risked their lives to come over here. They did it because they wanted freedom, and they wanted to be treated right by their government.”

The lawsuit has shone a harsh light on the government’s attack on an immigrant group that has received little attention as Ice has ramped up raids and escalated deportation efforts that were already expansive under Barack Obama.

‘The change in policy has been so abrupt and has really pulled the rug out from under a lot of these communities,’ says Phi Nguyen, litigation director at Advancing Justice-Atlanta. Photograph: Bloomberg/Bloomberg via Getty Images

Under a humanitarian agreement between the two countries, Vietnamese American refugees cannot be deported back to Vietnam if they entered the US before 1995, the year the two governments established diplomatic relations. Before Trump, that meant when the refugees, who became lawful permanent residents, faced deportation orders due to criminal convictions, Ice would not remove them or detain them indefinitely – it would instead release them under orders of supervision, the suit said.

The class-action suit seeks to represent all Vietnamese nationals who arrived pre-1995, are facing deportation and have been detained by Ice for more than 90 days. Attorneys are aware of nearly 40 refugees in that category, and about half of them have been detained for more than six months, the complaint said.

An Ice spokesman, Brendan Raedy, declined to comment on the lawsuit but told the Guardian that more than 8,600 Vietnamese nationals were currently subject to a “final” deportation order, and that more than 7,800 of them had criminal convictions.

“You cannot treat people like this,” said Lisa Dotson, sister of Hoang Trinh, a 41-year-old plaintiff who entered the US as a refugee at the age of four in 1980 and has been detained since last summer. “Tearing families apart and taking away members of the family, especially a father, it’s very hard. This doesn’t do any good for anybody.”

Trinh, whose family built a neighborhood bakery in California after fleeing Vietnam, is married with two teenage children and has no family in Vietnam. He is facing deportation due to a drug charge for which he served one year in prison, according to the suit.

Trinh has told his sister and attorney that he has been locked in a small cell for 23 hours a day, which has taken a toll on him: “You’re going to end up crazy if you stay there long enough,” said Dotson, 39, adding: “He’s missed a lot of big milestones. He missed his daughter’s graduation from high school.”

It was terrifying to think about what would happen if he were ultimately deported, the sister said: “I don’t know how the government in Vietnam would treat people like him.”

Dy Nguyen, who was working as a technician installing security systems when he was detained, fled Vietnam when he was three years old. His wife, Tammy, said three Ice agents had showed up to their Georgia home in November and initially made it seem as if they were taking him in for a minor paperwork issue.

The officers asked Tammy to get her husband a pair of socks and other belongings and told Dy, who was holding his daughter, to hand the baby to his wife, she recalled. Tammy said she was shaking as she held Chari while Ice took her husband away.

Dy is facing detention and deportation due to a 2010 burglary conviction. Tammy noted that he has already served his time and has since turned his life around – becoming active in church and youth groups and giving talks about his criminal past to help others learn from his mistake.

“Everybody deserves a second chance,” said Tammy, a 31-year-old medical assistant who came to the US from Vietnam when she was seven years old. “He’s a completely different man.”

She said she could not fathom a life for them in Vietnam: “Honestly, I think it would be a death sentence if he gets deported. We would have no way of living our lives.”

Raedy, the Ice spokesman, did not respond to questions about the specific cases, but he noted that Ice deported 71 Vietnamese nationals in 2017, double the number deported in 2016.

Ice has transferred Dy to a detention center even further away from his wife and daughter, who can no longer visit him in person. Now, they do video calls, which have become increasingly common in US jails and prisons.

Chari crawls to the computer when she hears her father’s voice and bangs on the keyboard: “She gets very excited every time she sees her dad.”

She doesn’t cry like she did inside the detention center. Chari, now nine months old, has gotten used to seeing her father on a screen.