Washington (CNN) The Trump administration plans to shift at least $155 million from the Federal Emergency Management Agency disaster relief fund to support its policy of returning some migrants to Mexico.

The Department of Homeland Security has informed Congress it will reprogram and transfer $271 million in total to its immigration enforcement agency from elsewhere in the department, including the FEMA money, according to documents obtained by CNN.

The moves comes as Tropical Storm Dorian nears hurricane strength as it approaches Puerto Rico.

Last week, the administration announced its intention to hold migrant families indefinitely, aimed at scrapping a settlement that put a 20-day limit on family detention.

DHS notified Congress of its plan to reprogram and transfer funds from agencies over to Immigration and Customs Enforcement, DHS' enforcement arm, on July 26, according to a DHS official. The department plans to transfer around $116 million for ICE detention beds, as well as transportation and deportation, the official said.

The department will not pull funds for detention beds from the US Secret Service, the Office of the Inspector General, and the Office of Intelligence and Analysis.

"In this case, this is a must-pay bill that needed to be addressed," said the official.

"We would not say that this is with no risk," said the official, who added that it was done in ways to "minimize the risk" to agencies that are losing funding.

FEMA said in a statement to CNN, "This transfer of funds to support the border emergency will leave a remaining balance of $447 million in the DRF (Disaster Relief Fund) Base account. Based on DHS and FEMA's review of historical emergency spending from the DRF Base account, this amount will be sufficient to support operational needs and will not impact ongoing long-term recovery efforts across the country. The DRF Majors account, which provides funding for ongoing recovery efforts, including those supporting communities impacted by the 2017 disasters, has a current balance of approximately $27 billion and is not impacted by the reprogramming."

It's not uncommon for departments, including DHS, to reprogram funds. DHS, in particular, has previously reprogrammed funds for detention beds, for example.

The reprogramming of money to Immigration and Customs Enforcement is sure to receive pushback from Democratic lawmakers who've criticized the agency.

In a letter to acting Homeland Security Secretary Kevin McAleenan, Democratic Rep. Lucille Roybal-Allard of California, chair of the House Homeland Security Appropriations Subcommittee, opposed the reprogramming of funds, saying she had "significant concerns about the intended use of funds" and the shifting of funds from other components.

House Homeland Security Chairman Bennie Thompson said in a statement that the administration is "flouting the law and Congressional intent to fund its extremist indefinite detention immigration policies."

"Taking money away from TSA and from FEMA in the middle of hurricane season could have deadly consequences. Congress should work to undo the damage this Administration is continually doing to our homeland security infrastructure," the Mississippi Democrat added.

DHS plans to transfer $23.8 million from the Transportation Security Administration for immigration enforcement, according to a document obtained by CNN.

Earlier this year, funds for additional detention beds -- as the administration has repeatedly pushed for -- became a sticking point in appropriations negotiations.

Democrats argued that by allowing ICE to up the number of detention beds, the agency would have the capacity to pursue a broader population of undocumented immigrants, including those without criminal records. But Republicans view the number of detention beds as central to limiting the release of detained undocumented immigrants into the US as they await hearings.

In the end, the spending bill included funding for an average 45,274 detention beds per day, with the intent to return to 40,520 by the end of the fiscal year, which is the level funded in the last fiscal year, but short of the administration's request of 52,000 detention beds. The reprogramming of funds will up ICE's bed count to roughly 50,000.

In recent months, however, the agency has been consistently holding more people in detention: As of August 10, 55,530 people were in immigration detention, according to the agency.

The latest shift in funds will also pull more money from FEMA -- $3.4 million for detention efforts.

Additionally, $4.3 million will be transferred from DHS' cyber agency.

DHS resources have been stretched thin amid an influx of migrants at the southern border. So far this fiscal year, more than 760,000 migrants have been arrested for crossing the border illegally. Many of them turn themselves in to agents.

In May, the Trump administration asked Congress for $4.5 billion in emergency funding. The request included additional detention beds. That part of the request was not fulfilled.