Washington — The Trump administration is planning to use $271 million allocated for disaster aid efforts and other initiatives to expand space in migrant detention centers and bolster a program that requires tens of thousands of asylum-seekers to wait in Mexico while their cases are processed in the U.S.

The Department of Homeland Security (DHS) notified Congress in late July that it intended to reprogram funds from several agencies — including the Federal Emergency Management Agency (FEMA), the Transportation Security Administration (TSA) and U.S. Coast Guard — to detention centers managed by Immigration and Customs Enforcement (ICE). It also said it was funding the construction of temporary facilities for the government to hold court hearings for its controversial "Remain in Mexico" program.

The notification to Congress was first revealed in a letter from Democratic Congresswoman Lucille Roybal-Allard, who chairs the House Appropriations Subcommittee on Homeland Security, to Acting DHS Secretary Kevin McAleenan. The California Democrat expressed her disagreement with his agency's plans.

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DHS notification to Congress, obtained by CBS News

"It is of great concern that during the course of this administration, there has been a growing disconnect between the will of Congress, as represented by ICE funding levels in enacted appropriations bills signed by the President, and the Department, immigration enforcement operations, which often lack justification," Roybal-Allard wrote in her letter, dated August 23.

Roybal-Allard said the proposed action by the sprawling department — which oversees two immigration-related agencies but also has important national security and disaster response responsibilities — would allow ICE to detain more people and carry out more removal operations. Over the past years, Congress has limited the number of detention beds through funding bills. Roybal-Allard accused DHS of attempting to circumvent those limits through its new plan to transfer funds.

DHS notified the committee that $116 million funds from different branches would go to finance the purchase of new beds for ICE, as well as operational needs. According to its notification to Congress, obtained by CBS News, DHS plans to gather this amount by taking funding from Customs and Border Protection's (CBP) operations budget, infrastructure projects and research for the Coast Guard, training and supplies for TSA employees, including Air Marshals, a cybersecurity initiative, an effort to counter weapons of mass destruction and other areas.

The agency also said it would divert $155 million from FEMA's Disaster Relief Fund so the government can establish facilities along the border for asylum seekers placed in the Migrant Protection Protocols (MPP) program and returned to Mexico.

Under the "Remain in Mexico" policy, migrants are only temporarily allowed back into the U.S. for the hearing. So far, the U.S. has placed more than 37,000 people in this program, CBP confirmed to CBS News on Tuesday. Migrants returned to Mexico in California and in the El Paso sector are scheduled for court hearings in San Diego and El Paso, respectively. But there are no immigration courts close to the Texas border cities of Brownsville and Laredo, the other locations where MPP has been implemented.

Because of this, the administration is looking to build "soft-sided facilities" in these parts of Texas. But Roybal-Allard noted that the country's immigration courts are overseen by the Executive Office for Immigration Review, a branch of the Justice Department, which she said is funded through separate congressional appropriations. She said using money to support those courts would seemingly violate federal law that "prohibits the obligation of funds from one appropriation account for a purpose if Congress has appropriated funds for that purpose through another account."

In a statement to CBS News, FEMA said the transfer of funds to "support the border emergency" will leave the agency with $447 million in funding for future disaster relief efforts. "This amount will be sufficient to support operational needs and will not impact ongoing long-term recovery efforts across the country," the agency added.

FEMA said the current pool of funding for ongoing recovery efforts, including those for natural disasters in 2017, will not be affected by the transfer. In its notification to Congress, DHS said the disaster relief funds left intact at FEMA will be sufficient to sustain operations "absent significant new catastrophic events."

But Democrats expressed concern about the transfer of FEMA funds during hurricane season and as Puerto Rico braces for Tropical Storm Dorian. Mississippi Representative Bennie Thompson, the Democratic chair of the House Homeland Security Committee, said DHS was "flouting the law" with its plan.

"This is reckless and the Administration is playing with fire — all in the name of locking up families and children and playing to the President's base leading up to an election year. Taking money away from TSA and from FEMA in the middle of hurricane season could have deadly consequences," Thompson wrote in a statement.

Senate Minority Leader Chuck Schumer of New York echoed Thompson's sentiments.

"The Trump administration's plan to divert money away from FEMA at the start of hurricane season to continue its efforts to separate and jail migrant families is backwards and cruel," Schumer wrote in a statement. "Taking these critical funds from disaster preparedness and recovery efforts threatens lives and weakens the government's ability to help Americans in the wake of natural disasters."

Earlier this year, the White House considered a proposal that would divert billions of dollars in disaster aid funds for Puerto Rico and several states affected by natural disasters to fund the construction of President Trump's long promised wall along the U.S.-Mexico border.