The Wisconsin state judge accused of impeding immigration agents at a Milwaukee courthouse last month pleaded not guilty on Thursday morning during a brief appearance in federal court.

Prosecutors have said that the judge, Hannah C. Dugan, violated federal law when she directed an undocumented defendant who was being sought by immigration agents through an alternate exit from her courtroom. Judge Dugan, who was indicted by a grand jury on Tuesday, is seeking the dismissal of the charges against her and has asserted that her actions were protected by judicial immunity.

A lawyer entered the plea on behalf of Judge Dugan, who was seated next to him in the federal courtroom on Thursday.

Protesters holding signs and chanting “Hands Off Judge Dugan” were gathered outside the downtown courthouse, and Milwaukee police officers blocked part of a street to accommodate the crowd.

“We know this isn’t about one judge,” Christine Neumann-Ortiz, the executive director of Voces de la Frontera, a Milwaukee-based immigrant rights group, told the crowd. “It’s an intimidation tactic.”

Inside the courthouse, the scene was far quieter. Judge Dugan arrived at the small, packed courtroom about 10 minutes before the hearing began. She shook hands with a federal prosecutor and smiled as she spoke quietly with her lawyers before a magistrate judge took the bench. Once the hearing began, she did not speak.