Lawyer Eric Dubelier leaves U.S. District Court, following the arraignment of Concord Management and Consulting LLC, one of three entities and 13 Russian individuals indicted in an alleged criminal and espionage conspiracy to tamper in the 2016 U.S. presidential election, in Washington, U.S., May 9, 2018. REUTERS/Yuri Gripas/File Photo

WASHINGTON (Reuters) - A U.S. judge said on Monday that a lawyer defending a target of Special Counsel Robert Mueller’s probe of Russian election meddling engaged in “unprofessional, inappropriate and ineffective” conduct, prompting the lawyer to say he might withdraw from the case.

Judge Dabney Friedrich told lawyer Eric Dubelier to stop what she called “meritless personal attacks” against Mueller’s team. Dubelier is defending Concord Management and Consulting LLC, a Russian firm accused of funding a propaganda operation to sway the 2016 presidential election in Donald Trump’s favor.

“I’ll say it plain and simple: knock it off,” Friedrich told Dubelier in U.S. District Court for the District of Columbia.

Dubelier said he needed to check with Concord to see if they still wanted him to work on the case, given that there appeared to be “some bias on the part of the court” against him.

In court filings, Dubelier has quoted movies such as “Animal House” and cartoon characters like Tweety Bird in criticizing Mueller’s long-running investigation as illegitimate and has sought to have the charges dismissed. Friedrich has twice refused to dismiss the charges against Concord.

Prosecutors contend that Concord is controlled by Evgeny Prigozhin, a businessman identified by Russian media as close to Russian President Vladimir Putin. U.S. officials have said Prigozhin has extensive ties to Russia’s military and political establishment.

Concord is one of three entities, along with 13 Russian individuals, indicted by Mueller’s office in an alleged criminal and espionage conspiracy to tamper with the 2016 U.S. election, boost Trump’s candidacy and disparage his Democratic opponent, Hillary Clinton.

Russia has denied any involvement. Trump has said there was no collusion between the Kremlin and his campaign, while repeatedly criticizing the Mueller probe as a “witch hunt.”