Charles Kupperman, President Donald Trump's former deputy national security adviser, filed a lawsuit Friday asking a federal judge to determine whether he is required to testify in the impeachment inquiry being conducted by the House of Representatives.

The outcome could affect the ability of other witnesses who worked closely with the president to cooperate with the ongoing investigation. The lawsuit was first reported by The New York Times earlier Friday.

Kupperman is scheduled to testify Monday. The scheduled interview would bring the inquiry closer into the orbit of John Bolton, Trump’s former national security adviser.

House Democrats are conducting an impeachment inquiry that centers on alleged pressure on Ukraine’s president to announce investigations into what has been called a conspiracy theory into the 2016 presidential election as well as into former Vice President Joe Biden and his son.

Critics say that amounts to an abuse of power by the president for personal political gain.

House Intelligence Committee Chairman Rep. Adam Schiff, D-Calif., leaves a secure area where Deputy Assistant Secretary of Defense Laura Cooper is testifying as part of the House impeachment inquiry into President Donald Trump, Wednesday, Oct. 23, 2019, on Capitol Hill in Washington. Patrick Semansky / AP

Kupperman says in the lawsuit that he was told by White House lawyers not to appear Monday.

The suit says the White House counsel informed Kupperman’s lawyer that "in order to protect the prerogatives of the Office of the President today and in the future, and in response to your request, the President directs Mr. Kupperman not to appear at the Committee's scheduled hearing on Monday, October 28, 2019.”

Kupperman says in the lawsuit that he is uncertain whether the subpoena issued by the House obligates him to appear and that he "is bound by his oath of office to abide by the lawful constitutional commands of both the President and the House of Representatives."

"It is not possible for Plaintiff to satisfy the commands of both the House Defendants on the one hand, and President Trump on the other," the suit says.

In a statement obtained by NBC News early Saturday, Kupperman's attorney said that his client "cannot satisfy the competing and irreconcilable demands of both the Legislative and Executive Branches."

"Under our system of Government, Constitutional disputes between the Legislative and Executive Branches should be adjudicated by the Judicial Branch, not by private citizens like Dr. Kupperman," his attorney, Charles J. Cooper, added.

Earlier Friday, a federal judge determined the impeachment inquiry is valid, despite arguments from the president and his allies that a full House vote was necessary to start the process.

"Even in cases of presidential impeachment, a House resolution has never, in fact, been required to begin an impeachment inquiry," wrote Judge Beryl Howell, the chief judge for the Washington, D.C. district court.

The White House counsel's office has refused to cooperate with the inquiry, arguing it's illegitimate because the House didn't hold a formal vote to declare one.

Howell in Friday's ruling also ordered the Department of Justice to turn over grand jury material referenced in redacted portions of special counsel Robert Mueller's report to the House Judiciary Committee. The Justice Department is expected to appeal.