Washington (CNN) The Justice Department said attempts by impeachment investigators to compel testimony from executive branch witnesses about President Donald Trump's dealings with Ukraine are "legally invalid" unless they allow for the witnesses to bring a government lawyer.

The guidance , from the DOJ's Office of Legal Counsel, amounts to a new legal reasoning that the White House and other agencies can use to stymie House depositions after Democrats curtailed the previous legal argument that the House wasn't in a formal impeachment inquiry with a vote last week . The memo is certain to anger Democrats as it furthers a strategy of non-cooperation from the White House in the inquiry, and once again puts the Justice Department in the position of blocking the President from further scrutiny.

Impeachment investigators had so far benefited from several depositions from current and former national security officials about the Ukraine saga, but in recent days, a number of current and former government witnesses, including former national security adviser John Bolton and a top national security aide to Vice President Mike Pence, have all skipped out on scheduled depositions.

In the memo, OLC lawyers write that the President, who has not been asked or subpoenaed to testify, must be allowed to have a representative present in depositions to be able to protect privileged information from disclosure. The House Intelligence Committee, which is leading the ongoing investigation, has so far only allowed witnesses to appear for depositions with personal counsel.

The five-page memo appears limited in scope but potentially sets up a future fight over the impeachment investigators' ability to pierce the administration's shield of executive privilege, which could block witnesses from providing valuable information about Trump's direct involvement in the case.

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