DALLAS (NewsNation Now) — The Biden administration is stepping up its effort to find and unite migrant families forcibly separated at the U.S.-Mexico border under President Donald Trump as part of the former president’s zero-tolerance policy on illegal crossings.

As of Tuesday, the final phase of the Central American Minors (CAM) program has been revived. The Biden administration says it’s the safest, most humane way to reunite parents and guardians with their children still living in Central America.

The Obama-era program allows families to be reunited under the following guidelines: The parents must be living lawfully in the United States, children must be unmarried, under 21 years old, and living in one of three countries — Guatemala, Honduras or El Salvador.

“It will send a message that coming into U.S. or trying to come into U.S. through irregular means is only going to hurt their chances of coming in later on,” said Naim Haroon Sakhia, an immigration attorney.  

“We want to make sure that they come through regular immigration channels rather than irregular, because when that happens we lose control,” Sakhia explained. “We don’t know who’s coming in, what they’re bringing in.”

The White House says it’s the best way to keep children from making the treacherous migration alone.

A joint statement released by the U.S. Department of State and Homeland Security reads, “We are firmly committed to welcoming people to the United States with humanity and respect, and reuniting families.”

The program was terminated under the Trump administration as part of the former president’s executive orders aimed at tightening immigration controls.

CAM has also been extended to include guardians. The child applying to the program must be at home in Central America. Families will not be approved for the CAM initiative if the child has already made the trek and is currently in Mexico or a border city.

While there’s no way to know concretely how many families this program might affect, many immigration experts say this is an opportunity to help tens of thousands of families be reunited.

When the program was shut down by Trump, there were over 3,000 pending applications that had to be closed. About half of them have been reopened, but no children have arrived in the United States at this time.