Former U.S. special envoy to Ukraine Kurt Volker, who resigned last week, will appear in a deposition on Thursday as part of the House Intelligence Committee's impeachment investigation, a committee official confirmed to Axios.

Why it matters: Secretary of State Mike Pompeo sent a letter to top House Democrats on Thursday claiming that the deposition dates they had scheduled for 5 former and current State Department officials were "not feasible." Former U.S. Ambassador to Ukraine Marie Yovanovitch, who was scheduled to appear on Wednesday, will now be appearing on Oct. 11 with the agreement of both the committees conducting the Ukraine investigation and her counsel, per the official.

The big picture: The whistleblower complaint that help set off House Democrats' impeachment investigation names Volker as one of the Trump administration figures potentially involved in Rudy Giuliani's alleged scheme to push Ukraine to investigate Joe Biden.

A day after the now-infamous phone call between Trump and Ukrainian President Volodymyr Zelensky, the whistleblower said that Volker and U.S. Ambassador to the EU Gordon Sondland met with Ukrainian officials and provided them with advice on how to "navigate" Trump's demands.

Go deeper: House chairs accuse Pompeo of "stonewalling" in Ukraine investigation