The United States will reimplement the Trump-era “Remain in Mexico” program as soon as Monday, the Department of Homeland Security said after the Mexican government agreed to allow migrants to stay there as they wait for their U.S. immigration court hearings.

The agency said Thursday it would relaunch the program formally known at the Migration Protection Protocols, or MPP, “on or around” Dec. 6. Once fully operational, the program will be implemented across the southwest border at seven ports of entry: San Diego; Calexico, Calif.; Nogales, Ariz.; and El Paso, Eagle Pass, Laredo and Brownsville, all in Texas.

Under MPP, migrants who cross the U.S.-Mexico border and request asylum are returned to Mexico and forced to wait there for final decisions in their U.S. immigration cases.

Mexico issued a statement earlier Thursday saying that, given the U.S. commitment to address its humanitarian concerns about MPP, “it will not return to their countries of origin certain migrants who have an appointment to appear before an immigration judge in the United States to request asylum in that country,” according to a translated version of the release.

The announcement came hours after DHS announced a series of changes to MPP to address Mexico’s concerns and said it was ready to restart the program as soon as the Mexican government “makes a final and independent decision” to accept migrants through the program. 

Human rights advocates panned the program while it remained in effect under the Trump administration for putting vulnerable asylum-seekers at further risk and limiting their access to U.S. immigration lawyers.

Mexico had raised similar concerns and requested improvements before the program could be reinstated, the government said in earlier court filings.

Under the changes announced Thursday, DHS committed to ensuring migrants will have access to lawyers before and during their initial screenings and at immigration court hearings and will receive more and better information about the border program. DHS also pledged that individuals will generally have final decisions in their asylum cases within six months of being returned to Mexico.

The U.S. government will also work with the Mexican government to ensure migrants can travel safely to their U.S. immigration court hearings, which may require people to go through Mexico late at night to make early morning hearings, and can access health care, work permits and safe shelters in Mexico.

Migrants will also have access to COVID-19 vaccines, DHS said.

The administration has faced blowback from immigrant advocacy groups and nonprofits, who say that no improvements to the program could cure its inherent flaws. In October, more than 70 legal services providers and law firms wrote a letter to top administration officials arguing there “is no way to make this program safe, humane, or lawful” and that they “refuse to be complicit” in it.

The planned revival of the controversial program is in response to a federal court ruling ordering the Biden administration to take good faith efforts to resume MPP.

The administration halted the program shortly after President Joe Biden took office, and formally terminated it in June. Following a lawsuit by Texas and Missouri challenging the termination, a Texas federal judge found the administration had not sufficiently explained its reasoning for ending the program.

While the administration works to resume the program under that court order, it has also moved to end it again. In October, DHS released a pair of memos re-terminating the program with more reasoning provided.

Homeland Security Secretary Alejandro Mayorkas concluded in those memos that while the implementation of MPP “likely contributed to reduced migratory flows,” it did so “by imposing substantial and unjustifiable human costs on the individuals who were exposed to harm while waiting in Mexico.”

However, the new termination memo won’t take effect until it is reviewed and approved by the judge.

Sen. Bob Menendez, D-N.J., chairman of the Foreign Relations Committee, said he was “deeply concerned” the administration was expanding MPP “before critical safeguards are in place.”

“We urge the Biden-Harris Administration to make every effort to reduce the harm of this court order and ensure the end of this xenophobic and anti-immigrant policy for good,” he said in a statement Thursday.

Eleanor Acer, senior director for refugee protection at Human Rights First, said MPP “was a humanitarian disaster when it was first implemented, and it is doomed to be so again.”

“A laundry list of improvements cannot fix an inherently inhumane, illegal, unjust, and unfixable policy,” she said in a statement.