NEW YORK (AP) — President Joe Biden hit Elon Musk for immigration hypocrisy following a published report that Tesla’s CEO once worked illegally in the United States. The South African-born Musk denies the allegation.

“The richest man in the world turned out to be an illegal worker here. No, I’m serious. He was supposed to be in school when he got a student visa. He wasn’t in school. He broke the law. And he’s talking about all these illegal aliens coming our way?’ Biden said at a union building during his campaign on Saturday in Pittsburgh.

The Washington Post reports this that Musk was working in the country illegally while on a student visa. Citing company records, former business partners and court documents, the newspaper said Musk arrived in Palo Alto, California, in 1995 for a graduate program at Stanford University “but never enrolled in any courses, working instead on his startup. ”

Musk wrote on X in response to a video post of Biden’s comments: “I was indeed allowed to work in the US.” Musk added: “The Biden puppet is lying.”

Investors in Musk’s company, Zip2, were concerned about the possibility of their founder being deported and gave him a deadline to obtain a work visa, according to the report. The newspaper also cited a 2005 email from Musk to his Tesla co-founders, in which he acknowledged that he was not authorized to be in the US when he started Zip2.

According to the report, that email was submitted as evidence in a now-closed defamation case in California, which alleged that Musk had applied to Stanford so he could legally stay in the country.

Musk is today the richest man in the world. He has has pledged more than $70 million to help Republican presidential candidate Donald Trump and other Republican candidates win on November 5, and is one of the party’s biggest donors this campaign season. He headlined events in the final stages of the race for the White House, often echoing Trump’s dark anti-immigration rhetoric.

Trump has promised to give Musk a role in his government if he wins next month.

There was no immediate response to messages left asking X and Tesla for comment from Musk.