Democrats are planning to subpoena Gordon Sondland, the United States ambassador to the European Union, after President Trump said he would not testify Tuesday morning because it’s a “kangaroo court.” “Ambassador Sondland’s testimony and documents are vital, and that is precisely why the Administration is now blocking his testimony and withholding his documents,” Chairmen Adam Schiff, Eliot Engel, and Eljiah Cummings said in a joint statement. Sondland, a key witness to Trump’s reported campaign to put pressure on Ukraine, was scheduled to appear before House Democrats Tuesday morning, but just hours before his appearance, he was ordered by the State Department to avoid the hearing.

Sondland is considered a key witness to Trump’s dealings with Ukraine because the president reportedly instructed him to take a lead in the relationship between the two countries. Trump later tweeted: “I would love to send Ambassador Sondland... to testify, but unfortunately he would be testifying before a totally compromised kangaroo court, where Republican’s rights have been taken away, and true facts are not allowed out.” The ambassador’s attorney said he is “profoundly disappointed” that he was prevented from appearing, and “stands ready to testify on short notice, whenever he is permitted to appear.”