In a letter to Sondland, the Democratic chairmen of three House committees said the subpoena compels him to appear on 16 October to answer questions on his role in US President Donald Trump's reported efforts to pressure Ukraine to probe a political rival.
According to a statement issued earlier on Tuesday by three Democratic chairpersons, "Ambassador Sondland’s testimony and documents are vital" for the ongoing impeachment inquiry into Trump's 25 July telephone call with Ukraine President Volodymyr Zelensky.
House Dems said in the statement that "Ambassador Sondland routinely spoke to the President and had conversations with both Trump and Zelensky before and after the July 25 call, noting in a July 26 television interview that he spoke to President Trump 'a few minutes before' President Trump made the July 25 phone call".
US Secretary of State Mike Pompeo earlier warned against intimidating and bullying "distinguished professionals of the Department of State” in the Trump-Ukraine probe.
The impeachment inquiry into Trump’s 25 July telephone call was initiated after a whistleblower sent a complaint to the US Congress claiming that Trump had pressed Zelensky to investigate possible corruption by 2020 Democratic US presidential candidate Joe Biden and his son Hunter Biden, and threatened to withhold financial aid to Ukraine.
Trump denied the allegations, suggesting that they were a political witch hunt intended to reverse the outcome of the 2016 US presidential election. The embattled US president then ordered a transcript of the telephone call with Zelensky to be declassified.
The transcript revealed that the US president asked Zelensky to work with the former's personal lawyer and the Trump-appointed US attorney general to "look into" whether Joe Biden, who "went around bragging that he stopped the prosecution" was involved in possible corruption in Ukraine. The purportedly complete transcription, however, did not contain signs that the US president overtly threatened to withhold financial assistance to Ukraine.
Hunter Biden and his father Joe Biden were embroiled in a political scandal beginning in 2016 after then-US Vice President Joe Biden publicly admitted that he had demanded - threatening to withhold $1 billion in US military aid to Ukraine - to fire the Ukrainian prosecutor general who investigated the business dealings of Biden's son in Ukraine.
The White House said in a statement on Tuesday that the Trump administration will not participate in what it is describing as "political theater".