Later on Tuesday, House Democrats issued a subpoena to Sondland compelling him to testify next Wednesday, October 16, and produce requisite documents.
The missive is the White House's latest response to intensifying impeachment efforts spearheaded by House Democrats, who launched the proceedings late last month accusing Trump of pressuring the President of Ukraine to probe into the activities of former Vice President Joe Biden and his son in the country. It literally means under penalty if you don't show up, there is a penalty - jailing and fines and that sort of thing.
When pressed about the allegations in a Friday interview, Warren told the Wall Street Journal, "I know that everyone wants to try to drag in other people. They will ignore those subpoenas at their peril".
It's the second time in recent days that Democratic lawmakers have floated the possibility of Trump administration officials going to prison. He had flown to Washington from Brussels to testify before the joint committee.
Sondland is further named in the intelligence community whistleblower repot that spurred the impeachment inquiry.
"The White House letter is only the latest attempt to cover up his betrayal of our democracy, and to insist that the President is above the law", said House Speaker Nancy Pelosi in a statement on Tuesday, adding the president had "normalize [d] lawlessness".
The White House will not participate in Congress' ongoing impeachment inquiry, it said Tuesday, stepping up a political and legal standoff between the executive and legislative branches of government.
Sondland, the hotelier appointed ambassador to the European Union after donating $1 million to Trump's inauguration in 2016, has emerged as a key figure in the Ukraine controversy, which was set off after Trump asked the Ukraine government to dig up dirt on Democratic Presidential candidate Joe Biden and his son Hunter.
He noted that shortly after the transcript was released, Schiff fabricated portions of the transcript during a House Intelligence Committee hearing, and that Schiff also misled the public about his office's contact with the whistleblower who filed a complaint against Trump over the phone call.
Whether Yovanovitch will appear has been thrown into question by the White House's assertion that it will not cooperate with what it now considers an illegitimate impeachment inquiry of the president.
Cipollone called for a vote by the full House. The American people have already heard the President's own words - 'do us a favor, though.' The President's actions threaten our national security, violate our Constitution and undermine the integrity of our elections.
The White House letter to Pelosi, Schiff and other House committee chairmen, though asserting a legal argument that Trump and other officials can not cooperate, would not be likely to win respect in court, said Stephen Vladeck, a law professor at the University of Texas.