A witness in U.S. special counsel Robert Mueller's investigation was cited for contempt on Friday after he refused a court order to appear for a grand jury.

Andrew Miller, a former aide to Roger Stone, last week was ordered to testify and provide documents subpoenaed by the Mueller-empaneled grand jury in U.S. District Court for the District of Columbia.

Miller served briefly as an assistant to Stone during the 2016 presidential campaign, reportedly handling media interviews. Stone is a longtime associate of President Donald Trump.

Miller did not appear for the grand jury, which prompted U.S. District Chief Judge Beryl Howell to hold him in contempt during a closed court hearing on Friday, said Paul Kamenar, one of his attorneys.

Miller agreed he was acting in contempt of the order Howell issued last week, "and we filed a motion to that effect," said Kamenar.

EPA USA ROGER STONE RUSSIA POL GOVERNMENT USA DC
Roger Stone, an associate of President Trump, speaks to the media after answering questions from the House Intelligence Committee's Russia probe in the U.S. Capitol in Washington, D.C., on Sept. 26, 2017.
Jim Lo Scalzo, epa

However, Howell stayed the contempt ruling until Monday, giving Miller's legal team an opportunity to appeal the ruling that ordered his grand jury appearance to the District of Columbia Circuit Court of Appeals.

Had the judge not issued the stay, Miller could have been jailed until he agreed to testify before the grand jury and provide the subpoenaed documents.

Kamenar said the appeal would allow Miller's legal team to continue arguments that Mueller was unconstitutionally appointed to investigate Russian interference in the 2016 presidential election and explore whether Trump or any of his associates conspired with that effort.

"There really is no clear statute that authorizes the appointment of independent counsels," the attorney said.

Miller's legal team will also argue that Mueller's power as an independent counsel "is so vast," and his supervision "is so minimal" that he should have been nominated by the president and confirmed by the U.S. Senate, said Kamenar.

Nonetheless, Howell's 93-page order that required Miller to appear before the grand jury said: "multiple statutes authorize the Special Counsel's appointment, and the official who appointed the Special Counsel had power to do so."

By ordering Miller to testify, Howell became the third federal judge to rule that the special counsel investigation being conducted by Mueller is lawful and constitutional. However, one outstanding challenge is continuing.

The reason for Mueller's subpoena of Miller has not been made public.

However, Mueller's investigation has focused on Stone, Miller's former boss, in part because Stone issued a series of public statements, posted tweets suggesting that he had advance knowledge of hacked Democratic emails that the group WikiLeaks released during the 2016 presidential campaign, several news organizations have reported.

Mueller has also called other Stone associates to testify. In response, Stone has accused Mueller's investigative team of harassment.

Contributing: Christal Hayes

Follow USA TODAY reporter Kevin McCoy on Twitter: @kmccoynyc