A US judge has said he could hold the Trump administration in contempt of court for "wilful disregard" of an order to halt the departure of deportation flights carrying more than 200 people to El Salvador last month.
The administration had invoked a 227-year-old law meant to protect the US during wartime to carry out the mass deportation.
"The Court does not reach such conclusion lightly or hastily; indeed, it has given Defendants ample opportunity to rectify or explain their actions. None of their responses has been satisfactory," federal judge James Boasberg wrote.
In a statement, the White House said it would contest the decision.
White House Communications Director Steven Cheung said: "We plan to seek immediate appellate relief", referring to a process in which parties can request a higher court review and potentially change a decision made by a lower court.
"The President is 100% committed to ensuring that terrorists and criminal illegal migrants are no longer a threat to Americans and their communities across the country."
Judge Boasberg's decision to begin contempt proceedings escalates a clash between the White House and the judiciary over the president's powers.
The administration could avoid a contempt finding, or "purge" itself of contempt, if they provide an explanation of their actions and come into compliance with the original order issued last month, Boasberg said on Wednesday.
That filing is due by 23 April, he said.
His ruling comes despite the Supreme Court's later finding that Donald Trump could in fact use the 1798 Alien Enemies Act to conduct the deportations to El Salvador.
The Supreme Court's ruling against Boasberg's temporary restraining order "does not excuse the Government's violation", he said.
If the administration does not provide the requested information by the 23 April deadline, Boasberg will then seek to identify the individual people who ignored the order to stop the deportations.
He could then recommend prosecutions for those involved. Federal prosecutions come under the US justice department which ultimately reports to the Trump administration.
The March deportation flights saw more than 200 Venezuelans accused by the White House of being gang members deported to a jail in El Salvador.
During a 15 March hearing, Judge Boasberg imposed a temporary restraining order on the use of the wartime law and a 14-day halt to deportations covered by the proclamation.
After lawyers told him that the planes had already departed, he issued a verbal order for the flights to be turned around to the US.
The White House denied violating the court ruling.
US press secretary Karoline Leavitt said: "The administration did not 'refuse to comply' with a court order.
"The order, which had no lawful basis, was issued after terrorist TdA [Tren de Aragua] aliens had already been removed from US territory."
After two deportation flights continued to El Salvador despite his order that they be turned around, Judge Boasberg convened a hearing to discuss "possible defiance" of his ruling by the Trump administration.
In response, Trump took to TruthSocial to call Boasberg a "troublemaker and agitator" and call for his impeachment.
El Salvador has agreed to take in the deportees in exchange for $6m (£4.6m).
Earlier this week, Trump met with El Salvdador's President, Nayib Bukele, at the White House, and expressed an interest in sending more deportation flights to El Salvador.
