The lawsuit was announced by Democratic Governor Andrew Cuomo, a long-time opponent of Donald Trump.
“The Trump administration’s policy to tear apart families is a moral failing and a human tragedy,” Cuomo’s statement said.
“We will not tolerate the Constitutional rights of children and their parents being violated by our federal government,” the statement continued.
On Twitter, Cuomo said at least 70 children are being held in detention centres in New York, a number expected to increase.
The Trump administration's policy to tear apart families is a moral failing and a human tragedy. We will not tolerate the Constitutional rights of children and their parents being violated by our federal government. This heartless policy must end once and for all.
— Andrew Cuomo (@NYGovCuomo) June 19, 2018
The state is basing its suit on a 1997 legal settlement in which basic standards were set for the treatment of children detained for immigration reasons.
The suit alleges those standards are not being followed by Trump.
US border agency, Immigrations and Customs Enforcement (ICE), has come under heavy criticism for its treatment of families at the US-Mexican border.
Last week, a Department of Homeland Security (DHS) spokesman said that nearly 2,000 minors were separated from 1,940 adults who crossed the US border without documents between April 19 and May 31.
Administration officials have claimed they are forced to break up the families to follow the law, but according to the Washington Post, “These claims are false” – there are no statutes that mandate separating children from families at the border.
Critics point out that the administration can simply end the “zero-tolerance” approach.
Trump’s policy has been condemned by human rights groups and US politicians, both Democratic and Republican.
Amnesty International has called the policy “nothing short of torture”.
On Tuesday, audio from one of the camps where children are being held was released by ProPublica, a non-profit media organisation.
Inside a detention center last week. Children separated from their parents wail and ask for help.
A Border Patrol agent booms above the crying. “Well, we have an orchestra here,” he jokes. “What’s missing is a conductor.”
— ProPublica (@propublica) June 18, 2018
In the seven-minute-long recording, children can be heard crying and asking for their parents.
According to ProPublica, the clip was obtained from prominent civil rights lawyer Jennifer Harbury, who was given the audio by an unidentified individual who recorded the children in a detention centre.