A federal judge held a witness in special Counsel Robert Mueller's probe of Russian interference in contempt of court for refusing to testify before a grand jury. According to the Washington Post, District Chief Judge Beryl Howell made the ruling on Friday after a sealed hearing to discuss Andrew Miller’s refusal to appear before the grand jury. Miller is a former aide to longtime Trump confidant Roger Stone.

After the hearing, Miller’s lawyer Paul Kamenar said Miller was “held in contempt, which we asked him to be in order for us to appeal the judge’s decision to the court of appeals.” Howell stayed her order while Miller’s legal team appeals the judge’s decision.

Earlier this month, Miller fought and lost a court battle to quash a subpoena after a judge issued a 93-page opinion saying Miller must testify before the grand jury.

According to the WaPo, the chairman of the National Legal and Policy Center, Peter Flaherty, a conservative nonprofit that is funding Miller’s legal fight, said Miller had refused to appear before the grand jury in response to a subpoena. Miller is in Missouri, Flaherty said.

Earlier in the day, Kamenar and Flaherty were seen entering Howell’s courtroom before she sealed it, and declined to comment on the proceeding. Kamenar spoke afterward, confirming it was a hearing held after prosecutors filed a motion to find the witness in contempt.

When a subpoenaed witness refuses to testify before a grand jury, that person can be held in contempt. In some cases, such a contempt finding can lead to a witness being sent to jail until the person agrees to testify.

Stone has been under Mueller scrutiny following a series of public statements and tweets he made during the 2016 campaign in which he appeared to suggest he had advance knowledge of hacked Democratic emails released by WikiLeaks.

Miller worked for Stone during the 2016 presidential campaign, handling duties such as setting up media interviews. He is one of at least a half-dozen of Stone’s associates to be called to testify. Others include his driver, John Kakanis, and a social media consultant, Jason Sullivan. Kristin Davis, who gained notoriety in the 2000s as the “Manhattan Madam” when she ran a high-end prostitution ring, is also expected to testify to the grand jury.

Stone has accused Mueller’s team of harassing his associates.