House Oversight Committee chairman Elijah Cummings, D-Md., invited White House senior adviser for policy Stephen Miller to appear before the panel next month, due to his involvement in the White House’s “troubling” immigration policies.

Cummings, who emphasized that he was inviting Miller to appear out of his own volition, argued it “made sense” for Congress to hear directly from Miller since he oversees all immigration and border affairs.

“I am offering you an opportunity to make your case to the Committee and the American people about why you — and presumably President Trump — believe it is good policy for the Trump Administration to take the actions it has, including intentionally separating children from their parents at the border to deter them from coming into the United States, transferring asylum seekers to sanctuary cities as a form of illegal retribution against your political adversaries, and firing top Administration officials who refuse orders to violate the law,” Cummings wrote in a letter to Miller on Wednesday.

The letter comes after the Trump administration reportedly discussed U.S. immigration authorities to discharge immigrant detainees into “sanctuary cities” that protect undocumented immigrants from deportation, in part to get back at Democrats.

After the White House said the proposal was “rejected,” Trump tweeted “we are indeed, as reported, giving strong considerations to placing Illegal Immigrants in Sanctuary Cities only.” He later said that states like California should receive an “unlimited supply” of illegal immigrants to see if the state remains “happy.”

Miller was allegedly involved and reportedly talked to ICE officials about the plan, according to the Washington Post . Congress was notified by two Department of Homeland Security whistleblowers.

Additionally, the Trump administration’s decision to impose a “zero tolerance” policy last year that to prosecute all illegal immigrants came under scrutiny after it resulted in thousands of children being separated from their accompanying adults as they were held in HHS custody.

Cummings requested Miller provide a response to the panel by April 24.