President Donald Trump has instructed former White House counsel Don McGahn not to comply with a subpoena from the House Judiciary Committee that sought to have McGahn testify before the committee on Tuesday.

The House Committee is seeking testimony from McGahn, as well as others close to Trump, as part of its own investigation into events surrounding the 2016 presidential election, specifically the question of whether Trump or members of his administration obstructed justice during the process of the Mueller investigation. Current White House counsel Pat Cipollone informed Committee Chairman Jerrold Nadler (D-N.Y.) by letter that “the President has directed Mr. McGahn not to appear at the Committee’s scheduled hearing.”

Cipollone further indicated that, according to guidance from the Justice Department, “Mr. McGahn is absolutely immune from compelled congressional testimony with respect to matters occurring during his service as senior adviser to the President.”

McGahn became a key witness during special counsel Robert Mueller III’s nearly two-year investigation into the 2016 Trump campaign when it surfaced that Trump had pressured McGahn to instruct then-Deputy Attorney General Rod Rosenstein to fire Mueller. According to Special Counsel Mueller’s report, McGahn resisted Trump’s efforts.

Just last week, Cipollone also rejected the House Committee’s requests for a broad range of information and private communications from within the Trump White House. In a 12-page letter, Cipollone responded to the committee’s requests, stating, “It appears that the Committee’s inquiry is designed, not to further a legitimate legislative purpose, but rather to conduct a pseudo law enforcement investigation on matters that were already the subject of the Special Counsel’s long-running investigation and are outside the constitutional authority of the legislative branch.”

Trump has said on multiple occasions that his administration will “fight all subpoenas,” while claiming that repeated investigations from Congress are politically motivated by Democrats as they prepare for the 2020 election cycle.