"The Department of Justice has provided a legal opinion stating that, based on long-standing, bipartisan, and Constitutional precedent, the former Counsel to the President cannot be forced to give such testimony, and Mr. McGahn has been directed to act accordingly", Sanders said in the release.
The US Justice Department (DOJ) ruled that Congress may not constitutionally compel the president's senior advisers to testify about their official duties. This testimonial immunity is "rooted in the constitutional separation of powers and derives from the president's independence from Congress".
McGahn was scheduled to appear before the House Judiciary Committee on Tuesday to testify about Special Counsel Robert Mueller's investigation into alleged Trump-Russian collusion and 2016 US presidential election interference.
Later on Monday, Nadler said in a statement cited by Reuters that the panel will meet on Tuesday as planned and "Mr. McGahn is expected to appear as legally required".
Another Democratic member of the House Judiciary Committee, David Cicilline, told reporters on Monday that an impeachment inquiry could be warranted if McGahn does not respond to a congressional subpoena to testify before the panel.
"Let me be clear, if Don McGahn doesn't testify it is time to open an impeachment inquiry", Cicilline told MSNBC. "The president has engaged in an ongoing effort to impede our ability to find the truth, to collect evidence to do our work".
Meanwhile, McGahn's lawyer William Burck said in a statement that former White House counsel will not appear before the House Judiciary Committee on Tuesday.
The committee is investigating whether Trump illegally obstructed the probe into alleged Russian interference in the 2016 US presidential election. In particular, Mueller’s report, which was released earlier in April, alleged that Moscow interfered in the 2016 election but said there was no evidence of collusion between Russia and the Trump campaign.
Democrats on Capitol Hill have said that the alleged order by the US president to fire Mueller and an alleged attempt to compel McGahn to lie about it could amount to crimes of obstruction.
Moscow has repeatedly denied interfering in US politics and said Mueller's report provides zero evidence to support allegations of Russian election meddling.