The American Civil Liberties Union filed a class-action lawsuit Friday accusing President Donald Trump's administration of separating hundreds of immigrant parents and children who are seeking asylum.

The lawsuit expands a legal challenge over the detention of a Congolese asylum-seeker whose 7-year-old child was put in federal foster care by border agents, and asks a judge to find family separation unlawful.

The practice appears particularly pronounced in West Texas, where lawyers have reported dozens of cases.

"Whether or not the Trump administration wants to call this a 'policy,' it certainly is engaged in a widespread practice of tearing children away from their parents," Lee Gelernt, deputy director of the ACLU's Immigrants' Rights Project, said in a statement.

An investigation by the Houston Chronicle in November identified 22 cases in Texas in which parents with no history of immigration violations were prosecuted for the misdemeanor crime of illegal entry and had their children removed to foster care.

The ACLU suit, filed in federal court in San Diego, argues that the separation violates parents' rights to due process because their children are removed without a hearing. The government released the Congolese woman this week but she has yet to be reunited with her child.

The Department of Homeland Security did not immediately respond to questions about the lawsuit. Its acting press secretary, Tyler Houlton, said in a statement about the Congolese woman last week that it does not currently have such a policy of separating parents and children.

"However, we retain the authority to do so in certain circumstances — particularly to protect a child from potential smuggling and trafficking activities," he said.

Immigrant parents and minor children are usually held together or released to await their cases in the backlogged civil immigration courts. A landmark 20-year-old federal settlement bars the prolonged detention of children and holds they should be kept with their parents.

But last summer, the government began ramping up criminal prosecutions of parents, forcing the removal of their children who cannot be kept in prison.

Read more: Trump moves to end 'catch and release', prosecuting parents and removing children who cross border

In Friday's filing, Michelle Brané, director of the migrant rights and justice program for the Women's Refugee Commission, a nonprofit in Washington D.C., said the group had found 426 cases of immigrant parents and children who have been separated, either because the adults were prosecuted or because they were split in immigrant detention.

Mayra Jimenez, director of the children's program at RAICES, an immigrant advocacy group, said in the suit that it had identified more than 100 such cases.

The government has declined to release its statistics, and the separations are difficult to track because they play out among three mammoth and opaque federal agencies — the Departments of Justice, Homeland Security and Health and Human Services, which cares for unaccompanied migrant children.

Most adults in immigration detention facilities do not have access to lawyers.

The filing Friday expands the case to include a Brazilian woman who told Border Patrol agents near El Paso last fall that she was seeking asylum, a refugee status granted to people who face persecution because of their race, religion, nationality, membership in a social group or political opinion.

She spent 25 days in jail for the misdemeanor crime of illegally entering the country, while her 14-year-old son was placed in federal foster care in Chicago.

She has been detained since September in an immigration facility in El Paso, and has only been able to talk to her son six times.

"If we cannot be released, I would like us to be detained together," the mother said in the lawsuit. "I worry about him constantly."

Such separations also include Blanca Vasquez, who told Border Patrol agents last October that she feared returning home and asked for a lawyer, according to federal records. Gang members in El Salvador had killed her husband, a sergeant in the military, and persecuted her sons.

Read more: Her husband murdered, her son taken away, a mother seeking asylum tells a judge, 'I have lost everything'

Vasquez told the Chronicle that federal officials removed her 13-year-old son without telling her where they were taking him. They put her in prison for two months while she awaited trial on the misdemeanor charge of illegal entry.

The public defender's office for the Western District of Texas argued it was a violation of her due process rights. The lawyers said Vasquez and four other Central American parents named in a separate lawsuit pleaded guilty only because they didn't know what the government had done with their children and wanted to quickly reunite with them.

A federal magistrate judge in El Paso agreed such concern could be a factor, but declined to dismiss the charges in November. The public defenders have appealed the case.

Supporters of reduced immigration say separating parents and children is sometimes necessary so that immigration officials can determine if they are actually related and not the victims of human trafficking.

"Immigration fraud in support of wider criminal conspiracies is a daily occurrence," Matt O'Brien, director of research at the Federation for American Immigration Reform, said in a statement. "Keeping children with their alleged 'parents' can often mean leaving them with criminal poseurs who wish to exploit them."

But Vasquez said she had her son's birth certificate and identification proving she was his mother.

She served out her federal sentence, and was transferred to immigration custody. An asylum officer in December determined she did not have a credible fear of returning home.

She was about to be deported when lawyers at ALDEA, a nonprofit in Pennsylvania, read about her case in the Chronicle and intervened.

In an unusual about-turn, the asylum office found in a second interview that Vasquez did in fact have a reasonable claim and an immigration judge ordered her released last month on a $7,500 bond. She was freed Thursday in El Paso, nearly five months after being detained, and will reunite soon with her son in New Orleans..

Immigrant advocates have called family separations "so fundamentally unconscionable it defies countless international and domestic laws on child welfare, human rights and refugees," according to a complaint filed with the Department of Homeland Security in December.

The United Nations convention on refugees, to which the U.S. is a signatory, holds that countries should not impose penalties on refugees who enter unlawfully to ask for asylum.

The Trump administration considered splitting up parents and children shortly after taking office. To discourage families from making the dangerous journey north, it threatened to prosecute parents who paid smugglers and separate families apprehended at the border.

The number of families crossing the U.S. southern border plummeted.

Facing intense criticism from advocates, then-Homeland Security Secretary John Kelly — now White House chief of staff — backed away, saying separations would occur only in extenuating circumstances such as illness.

But over the summer family arrivals began rising once more.

lomi.kriel@chron.com

Twitter: @lomikriel