President Donald Trump’s administration has reunited more than 1,000 parents with their children following its immigration policy under which families were separated at the U.S-Mexico border, but it told a federal judge on Tuesday it can no longer track hundreds of parents, NPR reports.

The administration will most likely meet a second deadline set by the judge to reunite immigrant families, according to data it submitted to the court.

Last month, U.S. District Judge Dana Sabraw told the government that it had a month to reunite over 2,500 kids between the ages of 5 to 17 with their parents.

The government’s lawyers said that as many as 463 parents may have been deported or voluntarily left the country without their children, per NPR.

In addition, according to NPR, Sabraw said that despite the government’s “remarkable achievement” of reuniting some families quickly, the ramifications of its immigration policy were a “deeply troubling reality.”

“The government says maybe some of them voluntarily agreed,” said Lee Gelernt, an attorney who works for the American Civil Liberties Union, NPR reports. “But until we speak to them, we have no idea what happened with these parents and why they left their children behind. We are hearing and we suspect that many of them will have been misled or coerced into leaving without their children.”