Three top House Democrats are demanding answers from the Trump administration on a White House proposal to release undocumented immigrants in so-called sanctuary cities to retaliate against President Donald Trump’s political rivals.

The chairmen of the House Committees on Oversight and Reform, the Judiciary, and Homeland Security set a May 3 deadline for Trump’s White House and DHS to deliver documents and communications about the proposal, which was reportedly devised and pushed by Trump immigration adviser Stephen Miller.

“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,” Chairmen Elijah Cummings (Oversight), Jerrold Nadler (Judiciary), and Bennie Thompson (Homeland Security) wrote in a letter Monday to acting White House chief of Staff Mick Mulvaney and Acting DHS Secretary Kevin McAleenan.

Nadler said on CNN’s “State of the Union” Sunday that whistleblowers told the Judiciary Committee “several weeks ago” that Miller had pushed the plan at DHS to release undocumented migrants into the so-called sanctuary cities — including the San Francisco district of Speaker Nancy Pelosi — to retaliate against Trump’s political rivals who oppose his immigration policy.

He was rebuffed when lawyers at the department said such a transfer of detained immigrants was illegal.