The White House has directed one of its former legal advisers not to testify to a congressional committee about special counsel Robert Mueller's investigation.
The Democratic-led House Judiciary Committee has issued a legal order for Donald McGahn to appear on Tuesday, the BBC reported.
A member of the committee said an impeachment inquiry against President Donald Trump would be warranted if McGahn does not testify.
McGahn told Mueller that Trump repeatedly tried to thwart his inquiry.
The Department of Justice and White House both released statements on Monday arguing that McGahn, the president's former counsel, was under no obligation to give evidence.
Later McGahn's lawyer said his client would "respect the president's instruction".
Mueller's two-year investigation did not determine that Trump conspired with alleged Russian attempts to sway the 2016 US presidential 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 McGahn has been directed to act accordingly."
In its memo, the justice department said 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."
But Judiciary Committee chairman Jerrold Nadler said Trump was trying to block damaging testimony about him obstructing justice.
"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.
The White House direction to McGahn, Nadler added, was "just the latest act of obstruction from the White House that includes its blanket refusal to cooperate with this committee."
Meanwhile, Representative David Cicilline, a member of the Judiciary Committee, said on Twitter: "If Don McGahn does not testify tomorrow (Tuesday), it will be time to begin an impeachment inquiry of" President Trump.
Also on Monday, a federal judge rejected Trump's efforts to block a subpoena into his accounting firm, Mazars USA LLP.
The subpoena, issued by the House Committee on Oversight and Reform on April 15, asked that the firm hand over financial records relating to Trump dating back to 2011, years before he announced his candidacy for president.
( 412 Words)