Former President Donald Trump escalated his longstanding feud with Mark Zuckerberg by threatening the Meta CEO with prison time.

Trump accused Zuckerberg of “plotting” against him during the 2020 election by “steering” Facebook against his campaign. Trump warned that if Zuckerberg were to do so again in the 2024 election, he would “spend the rest of his life in prison.”

The comments come in a new book authored by Trump called Save America. The book features photos from Trump’s term in office with captions describing the events. Trump’s threat against Zuckerberg was in a caption depicting a meeting between the two in the Oval Office.

Trump began by noting that Zuckerberg would visit him at the Oval Office. “He would bring his very nice wife to dinners, be as nice as anyone could be, while always plotting to install shameful Lock Boxes [sic] in a true PLOT AGAINST THE PRESIDENT. ”

He then accused Zuckerberg of acting disingenuously by praising him and then turning Facebook against his unsuccessful 2020 reelection campaign.

“He told me there was nobody like Trump on Facebook. But at the same time, and for whatever reason, steered it against me,” Trump’s caption continues. “We are watching him closely, and if he does anything illegal this time he will spend the rest of his life in prison—as will others who cheat in the 2024 Presidential Election.”

Meta and Winning Team Publishing, the publisher of Save America, did not respond to a request for comment.

Over the years Trump has made similar threats to other perceived enemies. During a debate in the 2016 election he memorably told former Secretary of State Hillary Clinton she’d “be in jail” if he was elected. Trump campaign rallies often featured the chant “lock her up” in reference to Clinton. At another rally in October 2022 Trump advocated for jailing a journalist in order to get them to reveal a source.

There is no evidence that Zuckerberg was involved in a plot against Trump while he was in office. Nor did Trump’s allegations cite any specific law that Zuckerberg may have broken. The mention of “Lock Boxes” appears to be a reference to a $420 million donation Zuckerberg’s charity made to fund election infrastructure during in 2020.

Trump has repeatedly feuded with Zuckerberg over the years. In July, Trump made the same accusations that Zuckerberg was interfering in elections.

“All I can say is that if I’m elected President, we will pursue Election Fraudsters at levels never seen before, and they will be sent to prison for long periods of time,” Trump wrote on Truth Social. “We already know who you are. DON’T DO IT! ZUCKERBUCKS, be careful!”

Zuckerberg attempted to extend an olive branch to Trump after the failed assassination attempt against him in July, praising his bravery. “Seeing Donald Trump get up after getting shot in the face and pump his fist in the air with the American flag is one of the most badass things I’ve ever seen in my life,” Zuckerberg said a few days after the shooting.

During an interview with Fox Business, Trump said Zuckerberg called him several times after the assassination attempt, including to tell him he wouldn’t be endorsing a Democrat. Meta noted he has refrained from endorsing either candidate, as he's done in prior elections.

Earlier this week, Zuckerberg waded further into politics, writing a letter to the House Judiciary Committee about Meta’s handling of government requests about COVID-19-related content in 2021. Senior officials from the Biden administration “repeatedly pressured” Meta to remove some types of COVID-19 content, “including humor and satire,” according to the letter.

“I believe the government pressure was wrong, and I regret that we were not more outspoken about it,” Zuckerberg wrote.

In the letter, he also mentioned the donations he made that provided things like staffing and training for local poll workers during the 2020 election which was severely impacted by the pandemic. In 2020, Zuckerberg’s philanthropic organization that he co-runs with his wife Priscilla Chan, the Chan Zuckerberg Initiative, made donations to the Center for Election Innovation & Research and the Center for Tech and Civic Life.

“We are doubling down on our commitment to ensuring that every qualified jurisdiction has the resources it needs to allow every eligible citizen to vote safely and have their vote counted,” Chan and Zuckerberg said in a statement at the time of their donation.

The Chan Zuckerberg Initiative did not respond to a request for comment.

The donations received backlash from conservative groups that mistook them as support for Joe Biden’s candidacy. For that reason, Zuckerberg said he would not make such donations in the 2024 election.

“Despite the analyses I've seen showing otherwise, I know that some people believe this work benefited one party over the other,” Zuckerberg wrote. “My goal is to be neutral and not play a role one way or another—or to even appear to be playing a role. So I don't plan on making a similar contribution this cycle.”

This story was originally featured on Fortune.com