A gag order has been issued by the federal judge overseeing the criminal case against former Trump campaign chairman Paul Manafort and his associate Rick Gates.

On Wednesday, U.S. District Court Judge Amy Berman Jackson issued a directive which prohibits comments to the media and the public by lawyers, defendants, and witnesses which “pose a substantial likelihood of material prejudice to this case.”

Jackson asked lawyers to make their arguments in court and “not on the courthouse steps.”

Jackson had already warned lawyers about discussing the case publicly after Manafort defense lawyer Kevin Downing stood in front of the media on Monday and declared that the charges against Manafort were “ridiculous” and said the president was correct to insist there was “no evidence the Trump campaign colluded with the Russian government.”

“This is a criminal trial, and it’s not a public relations campaign,” the judge warned.

Jackson’s order also applies to “potential witnesses.”

Manafort and Gates were arraigned in federal court in Washington last week on a 12-count indictment, the first known indictments to come from special counsel Robert Mueller’s investigation into allegations of Russian interference in the 2016 presidential race.

They are charged with money laundering and failing to register as foreign agents for the government of Ukraine. The charges stem from activity that is seemingly unrelated to the election or Russia, and both men have entered not guilty pleas.

The Department of Justice tasked Mueller with overseeing the federal investigation into Russia’s alleged meddling, and whether there was any collusion with the Trump campaign.