There have been at least 429 cases of immigrant parents being separated from their children in the past two years, according to a class-action lawsuit filed on Friday against the Trump administration.

The American Civil Liberties Union (ACLU) suit alleges the US government has violated due process for hundreds of asylum-seeking families by separating parents and children without a hearing and without showing the child would be endangered by staying with the parent.

Administration officials said last year they were considering implementing a family separation policy to deter asylum seekers. No such policy has been announced.

“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,” said Lee Gelernt, deputy director of the ACLU’s Immigrants’ Rights Project.

Immigrant rights groups said they had seen hundreds of parents separated from their children under the Trump administration and that they expected the practice to continue.

Michelle Brané, director of the Women’s Refugee Commission’s migrant rights and justice program, said her group had identified 429 cases of family separation from its own work and from legal service providers and social service agencies. Brané told the Guardian these cases, which include toddlers to young teenagers, happened “more or less” in the past 15 months.

“I have been informed at various times off the record, by government officials, that there are discussions and plans in place to expand the practice,” Brané said in a court declaration.

These cases included parents and children separated while being placed into immigration proceedings and others separated after the parent was prosecuted for immigration violations while seeking asylum, according to court documents. The suit also claims there is no process for parents to contest a separation.

In the lawsuit, a plaintiff identified as Ms C said she has not seen her 14-year-old son, J, since they arrived in the US in August 2017 to seek asylum. Ms C, who fled Brazil, said she has only spoken to J a few times by phone since the separation.

“I hope I can be with my son very soon,” Ms C said. “I miss him and am scared for him.”

In January, more than 200 child welfare, development, health and justice organizations, including the American Academy of Pediatrics and Unicef, warned that such separations can cause lasting harm to children.

“The psychological distress, anxiety and depression associated with separation from a parent would follow the children well after the immediate period of separation – even after the eventual reunification with a parent or other family,” the organizations said in a letter to the homeland security secretary, Kirstjen Nielsen.

The Department of Homeland Security (DHS), which oversees immigrant detention, does not comment on pending litigation.

In court documents, attorneys and rights groups acknowledged separation may be necessary in cases where it is suspected the adult and child are not related or the parent could pose imminent danger to the child. But they alleged the government had not demonstrated this was the situation for the hundreds of cases in the suit.

The lawsuit filed on Friday broadened a suit filed in late February that challenged the separation of an asylum-seeking mother from her seven-year-old daughter.

The woman, a Congolese citizen named as Ms L in court documents, has been separated from her daughter for four months. DHS released the mother from a San Diego detention facility on Tuesday, but she has not been reunited with her daughter, who was being held in Chicago.

In a letter to DHS sent on 2 March, Democratic Illinois senators Dick Durbin and Tammy Duckworth requested more information on how many children have been separated from their families since Trump took office, how long the separations have been and whether DHS plans to continue separating.

The senators said: “While we may have different views on many immigration policies, we hope you will agree that it is cruel and inhumane to separate a parent from her child and immediately bring a stop to this practice.”