The parents of 545 children who were separated at the U.S.-Mexico border under the Trump administration’s immigration crackdown in 2018 have since been deemed “unreachable,” according to a joint legal filing by the American Civil Liberties Union and the Justice Department.

The family separations — which came about under the “zero tolerance” crackdown by U.S. border officials in spring 2018 — affected more than 2,800 migrant families. Hundreds of children have since been reunited with families in their home countries, but many others remain in limbo in the United States because their parents can’t be found.

The hundreds of children who remain here may still be eligible for the court-ordered reunifications.

Judge Dana Sabraw of the U.S. District Court in San Diego ordered an end to the separations in June 2018, and while most parents were eventually reunited with their kids before deportation, hundreds more were deported without them, according to reporting by CBS News.

When tracked down by immigration advocates, many of these parents chose to have their children brought back to their home countries, but hundreds more waived their right to reunification by allowing the children to stay in the U.S. with other family members, CBS reported.

An additional 1,556 migrant children were separated from their parents between the summer of 2017 and June 2018, the U.S. government revealed in October last year.

That’s when immigration advocates fanned out to locate 1,030 parents whose contact information was saved by the government.

Sabraw ruled these families could still be eligible for reunification if they remained separated, CBS reported.

The parents of 485 of these children were located, however 545 minors remain without their loved ones, and efforts to reach them were ultimately futile.

One advocacy group called Justice in Motion has been working for months throughout Mexico and Central America to find the missing parents, but social limitations of the COVID-19 pandemic have hindered their efforts.

“Sadly we are still looking for hundreds of families who were separated years ago and will not stop until we find all of them,” Lee Gelernt, the top ACLU attorney in the case, told CBS News. “Some of these children were only babies when ripped away from their parents.”