US Democrats have ordered the White House to hand over documents as part of their impeachment probe into Donald Trump.
The documents relate to a phone conversation the American president had with Ukraine’s leader Volodymyr Zelensky on July 25.
Mr Trump stands accused of trying to coerce Mr Zelensky into investigating his Democratic rival Joe Biden.
An anonymous whistleblower flagged concerns over the call - which the US president has described as “perfect” - sparking formal impeachment proceedings.
In the latest twist in the saga, the three committees leading the probe have given the White House until October 18 to release official records of the call.
A redacted version was previously made public, but the Democrats are demanding further details.
In a letter to the White House, they accuse Mr Trump of "stonewalling" multiple requests for the records, leaving them with no alternative but to issue the formal written order.
“We deeply regret that President Trump has put us - and the nation - in this position, but his actions have left us with no choice but to issue this subpoena," the Democrats wrote.
Mr Trump said he would formally object to congress over the impeachment inquiry, saying the Democrats would regret launching it in the end.
"I really believe that they're going to pay a tremendous price at the polls," he said.
But the Democrats have accused Mr Trump of taking "a path of defiance, obstruction and cover-up", and warned that refusing to hand over the documents would amount to “obstruction".
This, in itself, is potentially an impeachable offence.
A separate request for records has also been sent to Vice-President Mike Pence, with Democrats asking him to clarify "any role you may have played" in Mr Trump's discussions with Ukraine.
Mr Pence has admitted listening in on the call.
