Republicans are criticizing the Biden administration’s move to begin admitting 25,000 migrants held in Mexico as part of a Trump-era policy that was a key plank in the former administration’s efforts to end "catch-and-release."

The Department of Homeland Security (DHS) announced Friday it would begin to process migrants placed in the Migrant Protection Protocols (MPP) next week. MPP, known as "Remain in Mexico" was a policy implemented and expanded in 2019 that kept migrants in Mexico as they awaited their immigration hearing.

The Biden administration estimates that around 25,000 individuals enrolled in the protocols still have active cases. 

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MPP was a central part of a broad strategy by the Trump administration to end "catch-and-release," by which migrants claiming asylum were detained and then released into the interior of the U.S. 

The Trump administration said it was an effective way of reducing a key pull factor that brought migrants to the border, but critics including President Biden described the policy as cruel and one that put migrants in danger by keeping them in Mexico.

"As President Biden has made clear, the U.S. government is committed to rebuilding a safe, orderly, and humane immigration system," Secretary of Homeland Security Alejandro Mayorkas said in a statement. "This latest action is another step in our commitment to reform immigration policies that do not align with our nation’s values." 

But Republicans have been horrified by a wave of reversals of Trump-era policies by the new administration -- including the halting of the border wall and attempts to implement a 100-day pause on deportations -- and have pointed to early signs of a brewing border crisis.

Rep. John Katko, R-N.Y., the ranking member on the House Homeland Security Committee, said that the move was "outrageous" at a time when Americans were being told to avoid travel and stay at home -- before predicting a surge in numbers at the border.

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"Those being re-processed south of our border by international organizations, who will determine their eligibility, will soon be released into U.S. communities as they get added to the 1,000,000+ immigration court backlog. Adjudication will take years," he said. "As more migrants catch wind of the reimplementation of 'catch-and-release,' the surge on our border will be unimaginable."

"As CBP encounters at the border top 3,000 a day on average, we have swiftly moved into the dangerous territory of the 2019 border crisis," he said. "The situation at the border, combined with the raging pandemic, has created a perfect storm of security, humanitarian, and public health concerns."

Fox News reported last week that Customs and Border Protection (CBP) has been forced to release some families into the interior of the U.S. amid an increase in migrant traffic and Mexico’s refusal to accept additional families with children under age 12 in areas where migrant camps grow increasingly large, overwhelming the shelter and services.

Last week, the U.S. said it would add 700 beds for unaccompanied minors at a shelter in Carizzo Springs, Texas, along with 500 additional beds at a processing facility in Donna, also in Texas.

Sen. Ted Cruz, R-Texas, on Friday said that the U.S. has a "humanitarian and security crisis at our southern border." 

"Effectively returning to catch and release -- as the Biden administration announced today -- could very well result in the release of COVID positive persons into the U.S., which will exacerbate the dual border and public health crises by making Texas border communities less safe and further straining local resources," he said.

In a nod to fears of a flood of migrants at the border, both DHS and the White House have been warning migrants not to come to the border. White House Press Secretary Jen Psaki on Wednesday warned potential migrants that "now is not the time to come" and said that "the vast majority of people will be turned away."  

It was a message echoed by DHS on Friday, which warned migrants that the announcement "should not be interpreted as an opening for people to migrate irregularly to the United States. 

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"Eligible individuals will only be allowed to enter through designated ports of entry at designated times," it added.  

Administration officials declined to name the ports of entry out of fear they may encourage a rush of people to those locations, according to The Associated Press

Fox News’ William LaJeunesse and Greg Norman contributed to this report, as well as The Associated Press.