Washington — House Democrats on Tuesday launched a probe into the Trump administration's controversial policy of requiring tens of thousands of asylum-seekers to wait in northern Mexico for their U.S. immigration court hearings.

The Democratic-led House Judiciary Committee demanded troves of documents and data related to the implementation of the so-called "Remain in Mexico" program, which U.S. officials have used to return more than 57,000 Latin American migrants to often dangerous Mexican border cities. Citing the squalid and precarious conditions faced by those in the program, as well as the difficulty of finding U.S.-based lawyers while in Mexico, the committee said a "comprehensive review" of the policy is warranted.

"We strongly believe that MPP is a dangerously flawed policy that threatens the health and safety of legitimate asylum seekers — including women, children, and families — and should be abandoned," lawmakers wrote in their letter to Acting Homeland Security Secretary Chad Wolf, referring to the policy by its official name, the Migrant Protection Protocols.

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The lawmakers asked Wolf to respond to their request for information by the end of the month. The committee requested documents about enforcement and expansion of MPP since December 2018; demographic data about those in the program; statistics about "fear of persecution" interviews conducted by asylum officers; information about asylum-seekers who were returned to Mexico despite being given protections by an immigration judge; and an unredacted version of an internal probe of the policy.

CBS News series on "Remain in Mexico"

The administration has praised the MPP program as an "effective tool" to curb unauthorized migration, pointing to seven consecutive months of lower apprehensions along the southern border. But advocates and even some of the asylum officers implementing the program have been withering in their criticism of Remain in Mexico, saying it violates international obligations against returning migrants seeking refuge to dangerous places.

Because of the program, tens of thousands of asylum-seekers from across Latin America who would previously have awaited hearings inside the U.S. are stranded in shelters and encampments in northern Mexico, including in crime-ridden cities like Ciudad Juárez and Matamoros, located in a region the U.S. government warns American travelers not to visit due to rampant violence. The group Human Rights First has denounced hundreds of reported kidnappings and assaults against asylum-seekers returned to Mexico by the U.S.

The House Judiciary Committee's letter on Monday, signed by Representatives Jerry Nadler, Zoe Lofgren, Pramila Jayapal, Sylvia Garcia, Joe Neguse, Debbie Mucarsel-Powell and Lou Correa, also underscored concerns about due process advocates have raised. A CBS News series over the summer detailed how the program makes it extremely difficult for migrants to secure U.S.-based lawyers generally needed for successful asylum claims. According to data by researchers at Syracuse University, only about 4% of migrants in the program have had lawyers represent them in proceedings in the U.S.

"The policy has nearly eliminated the already scarce due process protections available to asylum-seekers — such as access to counsel — further reducing the likelihood that legitimate asylum-seekers can obtain asylum," the lawmakers wrote.

The Department of Homeland Security did not respond to a request for comment on Tuesday's announcement and the committee's letter.