US Ambassador to the European Union Gordon Sondland at the US Capitol on October 28, 2019. Mark Wilson/Getty Images

Lt. Col. Alexander Vindman, the National Security Council's top Ukraine expert, is set to testify on Tuesday -- and his planned remarks appear to contradict previous testimony from Gordon Sondland, the US ambassador to the European Union.

What Vindman says: The statement says that in a July 10 meeting with Ukrainian and US officials, Sondland "started to speak about Ukraine delivering specific investigations in order to secure the meeting with the President," which prompted John Bolton to cut the meeting short.

Afterward, in a debriefing, Sondland "emphasized the importance that Ukraine deliver the investigations into the 2016 election, the Bidens, and Burisma."

"I stated to Amb. Sondland that his statements were inappropriate, that the request to investigate Biden and his son had nothing to do with national security, and that such investigations were not something the NSC was going to get involved in or push. Dr. (Fiona) Hill then entered the room and asserted to Amb. Sondland that his statements were inappropriate," Vindman's statement said.

What Sondland said: Vindman's account stands in contrast to Sondland's testimony about the meeting wherein he stated "if Ambassador Bolton, Dr. Hill, or others harbored any misgivings about the propriety of what we were doing, they never shared those misgivings with me, then or later."

Backing up Taylor: Notably, Vindman's accounting of the meeting matches the testimony of Bill Taylor, the top US diplomat in Ukraine, who told investigators Vindman and Hill had detailed the meeting to him.

"Specifically, they told me that Ambassador Sondland had connected 'investigations' with an Oval Office meeting for President Zelensky, which so irritated Ambassador Bolton that he abruptly ended the meeting, telling Dr. Hill and Mr. Vindman that they should have nothing to do with domestic politics. He also directed Dr. Hill to 'brief the lawyers,' " Taylor testified.