The Department of Justice said Monday it will appeal a decision handed down by a federal judge in Washington last week that ordered the government to turn over normally secret information collected by former special counsel Robert Mueller.

The fight is among those at the heart of the impeachment inquiry into President Donald Trump. An appeal was expected.

Chief Judge Beryl Howell of the U.S. District Court in Washington ordered the Justice Department on Friday to turn over grand jury materials to the House Judiciary Committee as part of the panel's impeachment investigation, noting that the materials could contain evidence of potentially impeachable conduct.

The ruling was significant also because it brushed aside arguments made by the president and his conservative allies that the impeachment probe was illegitimate. Howell, in her ruling, said the White House's refusal to comply with the impeachment process strengthened Democrats' arguments.

"Congress's need to access grand jury material relevant to potential impeachable conduct by a President is heightened when the Executive Branch willfully obstructs channels for accessing other relevant evidence," she wrote.