A judge fined Donald Trump $5,000 on Friday after threatening the former president with jail time over a “blatant violation” of a partial gag order in his $250 million New York fraud trial.

The judge warned that future violations will subject Trump to “far more severe sanctions” — including imprisonment.

“Incendiary untruths can and have led to serious physical harm,” Manhattan Supreme Court Judge Arthur Engoron said in court earlier Friday, before asking a defense lawyer to explain why Trump should not be punished or imprisoned.

Trump’s attorney apologized on his behalf, saying the violation was unintentional.

The judge’s admonition is the first time Trump has been threatened with consequences for violating court-ordered restrictions on his speech. Trump was not in court to hear the rebuke, having left New York on Wednesday after attending two more days of the civil trial.

Engoron imposed a narrow gag order in the case earlier this month, after Trump sent a social media post attacking the judge’s law clerk.

Engoron at the time ordered that the Truth Social post be deleted, and he barred Trump and other parties in the case from making public statements about his staff.

But the post remained up on Trump’s website, donaldjtrump.com, for more than two weeks, archived screenshots of the page show.

The left-leaning website MeidasTouch published an article Thursday about the not-deleted post. The Daily Beast reported that that article led attorneys on both sides of the trial to be notified about the post, which was ultimately removed Thursday night.

“Last night I learned the offending post was never removed from a website,” Engoron said in court on Friday morning, NBC News reported.

“This is a blatant violation of the gag order. I made it clear failure to comply will result in serious sanctions,” he said. “It remained on the Donald J. Trump campaign site and in fact it has been on there for the past 17 days, [and] it was removed late last night after an email from this court.”

“Incendiary untruths can and have led to serious physical harm,” Engoron said. “I will now allow the defendant to explain why this should not end up with serious sanctions or I could possibly imprison him.”

Defense attorney Christopher Kise told Engoron that the violation was “truly inadvertent” based on his understanding of the facts.

“The Truth Social post was taken down when the court asked,” Kise said, and Trump “never made any more comments about court staff, but it appears no one took it down on the campaign website.”

“It is unfortunate and I apologize on behalf of my client,” he said.

Engoron said he would take Kise’s remarks “under advisement,” but added that Trump “is still responsible for what appears on the site.”

“I want to make clear that Mr. Trump is responsible for the large machine, even if it is a large machine,” the judge said, according to NBC.

Michael Cohen, Trump’s former personal lawyer who expects to testify against him next Tuesday, said he doubted Kise’s explanation.

“Donald knows exactly what he is doing and any statements to the contrary are misguided,” Cohen said in a statement to CNBC. “It is all about his intent to intimidate. Plain and simple.”

The case brought by New York Attorney General Letitia James accuses Trump, his two adult sons, his company and top executives of fraudulently inflating the values of their assets to get tax benefits and advantageous loan terms.

Trump has denied wrongdoing, though Engoron has already found the defendants liable for fraud and ordered the dissolution of their New York business certificates. The trial aims to settle six other claims by James, who seeks $250 million in damages and wants to bar the defendants from running a business in New York.

Engoron’s gag order isn’t the only limit on Trump’s speech in legal matters. A federal judge in Washington, D.C., in mid-October imposed a partial gag order in special counsel Jack Smith’s criminal case accusing Trump of conspiring to overturn his 2020 election loss to President Joe Biden. Trump has pleaded not guilty in that case.

That gag order, which followed many posts by Trump attacking various parties in the case, barred him from publicly targeting the special counsel and potential witnesses. Trump’s attorneys are appealing that order.

— CNBC’s Dan Mangan contributed reporting.