More than 7,000 immigrant children have been ordered deported without appearing in court since large numbers of minors from Central America began illegally crossing the U.S. border in 2013, federal statistics show.

The high number of deportation orders has raised alarm among immigrant advocates, who say many of those children were never notified of their hearing date because of problems with the immigration court system.

In interviews and court documents, attorneys said notices sometimes arrived late, at the wrong address or not at all. In some cases, children were ordered to appear in a court near where they were initially detained, rather than where they were living, attorneys said.

“What was a border crisis has now become a due process crisis,” said Wendy Young, president of Kids in Need of Defense, an advocacy group.

In February, dozens of advocacy groups asked the government to temporarily stop issuing removal orders when a child fails to appear in court, and to reopen cases in which deportations were ordered.

Unprecedented numbers of immigrant children started showing up at the southern U.S. border in the fall of 2013. Many traveled without an adult and said they were fleeing rising gang violence in Honduras and El Salvador.