(CNN) The appointment of acting Attorney General Matthew Whitaker two weeks ago should have no effect on an ongoing court challenge that questions the constitutionality of special counsel Robert Mueller's appointment, the Justice Department argued in a new court filing Monday.

"The President's designation of Acting Attorney General Matthew G. Whitaker on November 7, 2018, has no effect on this case," which deals with an attempt to force a Roger Stone associate to testify before a grand jury, the special counsel's legal team wrote in the filing.

"Whitaker's designation neither alters the Special Counsel's authority to represent the United States nor raises any jurisdictional issue," the prosecutors wrote. "Nothing exceptional about this case warrants a departure from standard procedure."

The case involves Andrew Miller, an associate of Stone's who was subpoenaed earlier this year. He refused to testify before the grand jury, even after a trial-level judge ordered he must. The judge held Miller in contempt of court, so he has taken his case to the federal Court of Appeals. Generally, Miller seeks to invalidate Mueller's work. He argues that Mueller cannot subpoena him because the special counsel was not appointed by the President nor confirmed by the US Senate.

The Justice Department legal team, led by longtime federal lawyers currently working for Mueller, says Mueller was properly appointed last May by then-acting Attorney General Rod Rosenstein and continues to work at the discretion of Justice Department leadership.

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