The U.S. government may not meet a court-ordered deadline to reunite migrant parents with their children who were separated after illegally crossing the U.S.-Mexico border, according to court documents filed overnight.

The U.S. Department of Justice asked the U.S. District Court in San Diego to clarify if it would be breaching the court’s order if families were reunited after the deadline due to delays in confirming parentage.

The U.S. government is scheduled to update the federal judge in the San Diego case on the reunification process at a hearing at noon PDT (1900 GMT) on Friday.

Government agencies are deploying field teams to swab cheeks of children and adults in government custody and using outside laboratories for DNA testing to verify family members, according to the government’s court papers.

If parentage cannot be confirmed, the government said, it may not meet the court-ordered deadline for reuniting more than 2,000 children with their parents.

The separations have sparked a fierce outcry and numerous protests, part of a political firestorm over U.S. President Donald Trump’s “zero tolerance” immigration policy and beefed-up efforts to deter illegal U.S. entry.

But it reversed course last month after a groundswell of global opposition and said it would keep families together if possible.

U.S. Judge Dana Sabraw last month ordered that children under 5 years old be reunited with their parents by July 10, and for all children to be reunited by July 26.

He also ordered that parents have phone contact with their children by Friday.

All parents in the custody of U.S. Immigration and Customs Enforcement, and who are known to have children aged below 5, had phone contact with them, according to a court filing by Robert Guadian, an ICE official.

Guadian also said children under 5 are detained in 23 facilities across 13 states. ICE has moved 23 parents on commercial flights to be closer to such children in anticipation of reuniting them, according to Guadian.

On Thursday, U.S. Secretary of Health and Human Services Alex Azar told reporters “under 3,000” children are now under HHS care, including about 100 under the age of 5.

Advocacy groups including the ACLU, which filed the lawsuit, have questioned the government’s contention it may need more time to safely reunite families, and have raised concerns about whether it has a comprehensive plan to bring families together.

The government, in its filing overnight, said the process could further be delayed by steps that were required before parents could be reconnected with their children. In addition to DNA testing to verify parentage, the government said it would need to perform a criminal history check, and has reviewed 300 adults with about 1,400 more to go.

The government also said it wanted to assure that parents could provide for the child’s physical and mental well-being.

As a result, some cases may require more time than allotted by the court, officials said, asking the court for guidance.

“HHS anticipates, however, in some instances it will not be able to complete the additional processes within the timelines the court prescribed, particularly with regard to class members who are already not in government custody,” they wrote.

Reporting by Susan Heavey and Yeganeh Torbati; editing by Bernadette Baum and Richard Chang