President Trump has ordered that the staff of the National Security Council be significantly reduced as he seeks to fend off an impeachment inquiry sparked partly by a whistleblower complaint involving the NSC, Bloomberg reports. Five sources cited in the Bloomberg report confirmed the move, saying Trump’s request had been handed down to top agency officials by acting White House Chief of Staff Mick Mulvaney and National Security Adviser Robert O’Brien. Two of the sources said the staff reduction stemmed from a desire to boost efficiency as O’Brien transitions into his new role as national security adviser.

The National Security Council, which currently employs just over 300 people, was mentioned in the whistleblower complaint over Trump’s dealings with Ukraine that triggered an impeachment inquiry. The whistleblower, an anonymous member of the U.S. intelligence community, alleged that NSC officials had tried to keep a controversial July phone call between Trump and Ukrainian President Volodymyr Zelensky under wraps by storing it in a secret computer system with highly restricted access. Trump has also apparently subscribed to claims that the whistleblower was a member of the NSC, retweeting an assertion late Friday that the whistleblower worked on the NSC’s Ukraine desk under former President Obama.