(Bloomberg) -- Three House committee chairmen are demanding to see internal White House and Homeland Security communications related to President Donald Trump’s proposal to release migrants apprehended at the southern border into so-called sanctuary cities across the U.S.

"These reports are alarming," wrote Judiciary’s Jerrold Nadler, Oversight and Reform’s Elijah Cummings, and Homeland Security’s Bennie Thompson, in a letter Monday to acting White House Chief of Staff Mick Mulvaney and acting Homeland Security Secretary Kevin McAleenan.

The three Democrats wrote that they are believe the administration lacks the legal authority to transfer detainees in such a manner. They demanded the documents by May 3.

The three pointed to multiple reports of plans to send the migrants to largely Democratic municipalities that prevent their police from cooperating with federal immigration authorities. It isn’t clear how such a program would be carried out, including how the migrants would be kept from leaving those areas.

On Friday, Trump tweeted, "Due to the fact that Democrats are unwilling to change our very dangerous immigration laws, we are indeed, as reported, giving strong considerations to placing Illegal Immigrants in Sanctuary Cities only."

‘Extensive Review’

Sarah Sanders, the White House press secretary, confirmed Sunday on ABC’s "This Week" that the administration is "doing a full and thorough and extensive review."

"The president likes the idea, and Democrats have said they want these individuals into their communities, so let’s see if it works and everybody gets a win out of it," she said.

In their letter Monday, Nadler, Cummings and Thompson said, "Not only does the administration lack the legal authority to transfer detainees in this manner, it is shocking that the president and senior administration officials are even considering manipulating release decisions for purely political reasons."

Citing news reports, the three wrote that "the plan appears to have been specifically designed to target Democratic districts," and that it runs against Immigration and Customs Enforcement policy guidelines and legal advice.

The chairmen demanded that the administration produce emails and other communications between the White House and Homeland Security officials "concerning such a transfer or release of immigration detainees to or in specific locations of the U.S."

They also want all internal communications between Department of Homeland Security officials on the topic, as well as documents "discussing political and legal justifications of such a move."

When a plan to move detainees to "sanctuary cities" was reported Thursday by the Washington Post, the White House and the Department of Homeland Security said the proposal had been rejected and was no longer under consideration. That changed when Trump issued his tweet on Friday.

Trump has previously threatened to cut off federal funding for local governments that adopt policies protecting undocumented immigrants.

To contact the reporter on this story: Billy House in Washington at bhouse5@bloomberg.net

To contact the editors responsible for this story: Joe Sobczyk at jsobczyk@bloomberg.net, Laurie Asséo

©2019 Bloomberg L.P.