"The first thing we are going to do we're going to have to hold McGahn in contempt", Nadler told CNN, adding that the panel would then move to enforce the contempt citation before launching court proceedings.
Earlier in the day, White House Press Secretary Sarah Sanders said that US President Donald Trump had instructed McGahn to defy a congressional subpoena and not attend Tuesday's scheduled hearing before the House Judiciary Committee. Late on Monday, McGahn's lawyer confirmed that the former White House counsel would not testify in front of the committee.
House Judiciary Committee Chairman Jerrold Nadler said last week that he was prepared to have a vote on whether to hold McGahn in contempt of Congress should he not show up for testimony.
READ MORE: Trump Says Doesn't Think He Can Let Ex-WH Counsel McGahn Testify Before Congress
The House panel is investigating whether Trump obstructed justice amid US Special Counsel Robert Mueller's investigation into allegations of Trump-Russia collusion.
Mueller’s report, released in April, concluded that Russia interfered in the 2016 election but said there was no evidence of direct collusion between Russia and the Trump campaign. Moscow has repeatedly denied interfering in US politics and noted that Mueller's report provides no evidence to support allegations of Russian election meddling.
The US attorney general has claimed that evidence provided in the Mueller report is insufficient to constitute an obstruction of justice offense.
READ MORE: Trump Says Russia Probe Not Part of Decision on White House Counsel McGahn
