The White House has told a former adviser not to testify about Special Counsel Robert Mueller's investigation, sparking outrage from Democrats, reports BBC.
Lawyer Donald McGahn previously told the investigation into Russian interference in the 2016 election that he had felt pressured by President Donald Trump to fire Mr Mueller.
Mr McGahn has been ordered to appear on Tuesday.
But the White House has now directed him not to speak to the committee.
A letter to the Democratic-led House Judiciary Committee said lawyer Donald McGahn was "absolutely immune from compelled Congressional testimony".
There are calls for an impeachment inquiry against President Trump if he does not testify.
Mr McGahn served as White House counsel for nearly two years before his resignation in October 2018.
Both the Department of Justice and White House released statements on Monday arguing that Mr McGahn was under no obligation to give evidence.
Later Mr McGahn's lawyer said his client would "respect the president's instruction".
Mr Mueller's two-year investigation did not determine that Mr Trump conspired with alleged Russian attempts to sway the 2016 election, but listed 10 instances of possible obstruction of justice by the president.
White House press secretary Sarah Sanders said Democrats did not like the conclusions of the Mueller report and wanted "a wasteful and unnecessary do-over".
Citing the justice department guidance, her statement added: "The former Counsel to the President cannot be forced to give such testimony, and Mr McGahn has been directed to act accordingly."
Sarah Sanders said the White House had been "completely transparent with the Special Counsel's investigation"
In its memo, the justice department said Mr McGahn did not have to testify.
Assistant Attorney General Steven Engel said: "Congress may not constitutionally compel the president's senior advisers to testify about their official duties."
Speaking to CNN, Judiciary Committee chairman Jerrold Nadler said the panel would hold Mr McGahn in contempt of Congress for not testifying.
Earlier, he said the instruction was "just the latest act of obstruction from the White House that includes its blanket refusal to cooperate with this committee".
"The president acted again and again - perhaps criminally - to protect himself from federal law enforcement. Don McGahn personally witnessed the most egregious of these acts," he said in a statement.
However, Mr Nadler and House Speaker Nancy Pelosi are coming under growing pressure from their party to launch an impeachment inquiry against the president.
US media reports suggest several member of the Judiciary Committee tried to convince Ms Pelosi to start such an investigation to make the Trump administration comply with subpoenas.
Representative David Cicilline, a committee member, said on Twitter: "If Don McGahn does not testify tomorrow [Tuesday], it will be time to begin an impeachment inquiry of" President Trump.
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