ABC News April 15, 2019

House Democrats investigating proposal to send undocumented immigrants to sanctuary cities

WATCH: WH says sanctuary cities plan 'on the table'

House Democrats are formally launching an investigation into the Trump administration's consideration of a controversial proposal to send undocumented immigrants to sanctuary cities.

The chairmen of the House Judiciary, Oversight and Homeland Security Committees have asked the White House and Department of Homeland Security for any communications concerning the potential transfer and release of immigrants detained at the southern border to various cities across the country.

They have also asked for any DHS memos or drafts of legal justification for the proposal.

(MORE: Trump's 'sanctuary cities' plan not first choice, but an 'option on the table': Sarah Sanders)

White House press secretary Sarah Sanders said Sunday on "This Week" the potential plan to transfer undocumented immigrants from border cities to "sanctuary cities" is "an option on the table," though it's not the administration's first choice. Trump tweeted Saturday about the plan, claiming, without citing any evidence, that the federal government “has the absolute legal right” to transfer undocumented immigrants into “sanctuary cities” after they legally have to be released from detention.

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White House Press Secretary Sarah Huckabee Sanders calls on reporters during a news conference at the White House, Sept. 10, 2018, in Washington, DC.

However, the chairman of the House Homeland Security Committee, Rep. Bennie Thompson, D-Miss., told ABC News Chief Anchor George Stephanopoulos on Sunday that he didn't see a legitimate way for the administration to implement a possible proposal to release undocumented immigrants into “sanctuary cities."

(MORE: No legal way to release immigrants into 'sanctuary cities': Rep. Bennie Thompson)

Administration officials had previously said the plan to transfer immigrants to "sanctuary cities" that don't comply with federal enforcement of immigration law was originally "floated and rejected."

"These reports are alarming. 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," Reps. Jerry Nadler, Elijah Cummings, and Thompson wrote in a letter.

The committee, which is asking for any communications between November 2018 and April of 2019, asked the White House to respond to the request by May 3rd.

In an interview on CNN Sunday, Nadler, the chairman of the House Judiciary Committee, disputed Trump's "absolute right" to carry out the policy.

"The president has no right to spend money appropriated by Congress for other purposes to ship immigrants all over the country," he said.

He also said the committee had heard from whistle-blowers on the policy and expected his committee would question White House aide Steven Miller, the president's advisor most closely associated with his hardline views on immigration.