Rudy Giuliani won't comply with a congressional subpoena as part of the House impeachment inquiry into President Donald Trump, an attorney for Giuliani told House investigators in a letter on Tuesday.

Giuliani, the president's personal lawyer, had been subpoenaed for documents related to his work in Ukraine, which has come under intense scrutiny after Trump asked the Ukrainian president to investigate former Vice President Joe Biden and his son Hunter. Last week, two of Giuliani's business associates who had been assisting him in his Ukrainian venture were arrested on campaign-finance charges.

Jon Sale, Giuliani's attorney for the subpoena, wrote that the former New York City mayor "will not participate because this appears to be an unconstitutional, baseless and illegitimate 'impeachment inquiry.'" Sale called the subpoena "overbroad, unduly burdensome, and seeks documents beyond the scope of legitimate inquiry."

Asked by ABC News what would happen if House Democrats decide to enforce the subpoena, Giuliani said "we will see what happens."

I will not participate in an illegitimate, unconstitutional, and baseless “impeachment inquiry.”



Jon Sale, who is a lifelong friend, has represented me for the sole purpose of analyzing the request and responding. At this time, I do not need a lawyer. pic.twitter.com/l0IR0ikEHD — Rudy Giuliani (@RudyGiuliani) October 15, 2019

On Monday, House Intelligence Chairman Adam Schiff, D-Calif., said "there have been real breaks, significant breaks in the White House firewall" despite the Trump administration's efforts to stonewall the impeachment inquiry. That said, Schiff said he and his Democratic colleagues expect the administration to "stonewall us" on issues more within the administration's control.

An official working on the impeachment inquiry told NBC News, "Witnesses do not get to choose whether to comply with a duly-authorized subpoena, or to pick their investigators — not in the justice system, not in the Congress, and not in our democracy."

"If Rudy Giuliani and the President truly have nothing to hide about their actions, Giuliani will comply—otherwise, we will be forced to consider this as additional evidence of obstruction, and may infer that the evidence withheld would substantiate the accusations of President Trump’s misconduct and efforts to cover it up," the official continued. "Nobody is above the law, not a president, and not his shadow envoy to Ukraine."

Separately, former Texas Rep. Pete Sessions said that he is cooperating with Manhattan prosecutors in a case that relates to Giuliani and his associates.

"Mr. Sessions is cooperating with the US Attorney from the Southern District of New York and will be providing documents to their office related to this matter over the next couple of weeks as requested," a spokesman for Sessions said.