Tens of thousands of migrants are gathering on the Mexican side of the southern border, ahead of the Biden administration’s planned re-implementation of the Trump-era “Remain in Mexico” policy which kept migrants in Mexico for their hearings.

Border Patrol sources told Fox News that as many as 60,000 migrants are amassing on the Mexican side and intend to enter the U.S. in the coming days, knowing that the Biden administration intends to re-implement the Trump-era policy next month in response to a court order from a federal judge that was upheld by the Supreme Court.

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Migrants already coming across in La Joya, Texas were predominantly from Honduras, Nicaragua, El Salvador and Guatemala and included many unaccompanied minors and single mothers. One woman told Fox that the economy in her country was terrible and as a single mother she cannot afford to send her child to school.

“Remain in Mexico,” formally called the Migrant Protection Protocols (MPP), was established and expanded in 2019 by the Trump administration and involved sending migrants back to Mexico, rather than being released into the U.S., as their immigration proceedings were heard. The Biden administration began unraveling it earlier this year, even amid soaring migrant numbers, and formally ended it in June before the court ruling ordered a reversal.

Proponents described the policy as incredibly effective and one that helped end the process of “catch and release.”

“That program alone resulted in a 75-80% reduction in families illegally entering the country. It closed that loophole down,” former acting Customs and Border Protection (CBP) Commissioner Mark Morgan said at a roundtable this week.

However, critics called the process inhumane and one that left migrants open to violence and exploitation on the Mexican side of the border by cartels and other criminals. Immigration activists have fumed at the Biden administration’s panned restart of the policy.

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In a filing last week, the Biden administration said it had made “substantial progress” in re-implementing MPP, even as it says it is seeking alternative ways to end the program.

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The filing said it had engaged in talks with Mexico, finalized operational plans and has also issued a task order to rebuild the soft-sided facilities (which were commonly referred to as “court tents”) in Laredo and Brownsville, Texas to the tune of $14.1 million — with a predicted $10.5 million a month in operational costs.

“As a result of this progress, DHS anticipates being in a position to re-implement MPP by mid-November dependent on decisions made by Mexico,” the filing said, even as a separate statement said that DHS is finalizing a memo that would end the policy in accordance with the order.

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The battle over MPP comes as leaks from government sources say that Fiscal Year 2021 set a record for apprehensions at the border, with 1.7 million encountered — 132,000 of those were unaccompanied children.

The final border numbers have not been released, but are expected any day.