The White House is denying a request from the House Oversight and Reform Committee for senior adviser Stephen Miller Stephen MillerSpecial counsel investigating DeVos for potential Hatch Act violation: report Trump confirms another White House staffer tested positive for COVID-19 Biden pick creates furor, underscoring bitterness over Obama immigration policy MORE to testify before the panel, according to reports.

Rep. Elijah Cummings Elijah Eugene CummingsBlack GOP candidate accuses Behar of wearing black face in heated interview Overnight Health Care: US won't join global coronavirus vaccine initiative | Federal panel lays out initial priorities for COVID-19 vaccine distribution | NIH panel: 'Insufficient data' to show treatment touted by Trump works House Oversight Democrats to subpoena AbbVie in drug pricing probe MORE (D-Md.), the committee’s chairman, reportedly received a letter from the White House late Wednesday refusing his request for Miller to appear before the panel to testify on the Trump administration’s immigration policies.

“We are pleased that the Committee is interested in obtaining information regarding border security and much needed improvements to our immigration system,” White House counsel Pat Cipollone wrote in the letter, which was obtained by The Washington Post and reported by other news outlets.

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Cipollone added that he could make “Cabinet secretaries and other agency leaders” available to discuss the issue.

The White House and Cummings did not immediately respond to requests for comment from The Hill.

Cummings first invited Miller to testify before the House panel last week, saying Miller is “one of the primary moving forces behind some of the most significant — and in my view, troubling — immigration policies coming out of the Trump White House.”

Cummings requested that Miller respond to his invitation by April 24.

Miller has pushed for hard-line immigration policies in the Trump administration, emerging as a key player amid recent turnover at the Department of Homeland Security. President Trump Donald John TrumpBiden on Trump's refusal to commit to peaceful transfer of power: 'What country are we in?' Romney: 'Unthinkable and unacceptable' to not commit to peaceful transition of power Two Louisville police officers shot amid Breonna Taylor grand jury protests MORE has praised Miller but denied that he has driven the administration's immigration policy.

The aide was reportedly behind several of the White House's controversial immigration policies, including sending migrants to “sanctuary cities” and orchestrating the White House’s so-called zero tolerance policy, which led to the separation of thousands of migrant families, according to the Post.

The move by the White House is likely to escalate tensions between the Trump administration and Cummings after a week of feuding. The administration and the Trump Organization defied three of Cummings's subpoenas this week and have continued to push back on other demands, including suing Cummings to try to block a subpoena requesting financial records from Trump’s accountant.

As a senior White House aide, Miller is not accountable to Congress in the same capacity as a Senate-confirmed Cabinet secretary, the Post noted. White House staff traditionally do not testify before Congress.

Updated 11:23 p.m.