In the latest twist in Elon Musk’s will-he-or-won’t-he Twitter buyout saga, the billionaire is demanding hard proof of the social network’s assertion that less than 5% of its users are fake accounts or spam bots — and he said the deal cannot “move forward” until Twitter does so.

Without citing any evidence for his claim, Musk tweeted that Twitter’s user base could represent “20% fake/spam accounts,” four times what the company claims, and it “could be *much* higher.” He referred to Twitter CEO Parag Agrawal’s reply Monday to Musk’s assertion about fake/spam accounts, in which Agrawal said in part that “Unfortunately, we don’t believe that this specific estimation can be performed externally, given the critical need to use both public and private information (which we can’t share).”

“My offer was based on Twitter’s SEC filings being accurate. Yesterday, Twitter’s CEO publicly refused to show proof of <5%. This deal cannot move forward until he does,” Musk tweeted early Tuesday.

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As Agrawal pointed out, Twitter has disclosed its estimate that spam and fake accounts represent less than 5% of its active users for years — including in its IPO filing. Wall Street has viewed Musk’s sudden latching on to questioning the sub-5% spam/bot metric as an attempt to either bail on the $44 billion acquisition or to drive the deal price down.

Twitter shares were down 1.3% Tuesday, to under $37/share — more than 30% below Musk’s $54.20/share offer price, as investors see a greater possibility that the deal won’t happen.

On Monday, Musk, speaking at a Miami tech conference, said a deal for Twitter at a lower price wasn’t “out of the question,” Bloomberg reported. “Currently what I’m being told is that there’s just no way to know the number of bots,” the mega-billionaire CEO of Telsa and SpaceX said at the conference. “It’s like, as unknowable as the human soul.”

Last week Musk said his deal for Twitter was “temporarily on hold,” citing the need to conduct due diligence on Twitter’s fake/spam accounts claim. He also said he was “still committed to [the] acquisition.”

Musk has said he wants Twitter to authenticate “all real humans” on the platform and tweeted last month, “If our Twitter bid succeeds, we will defeat the spam bots or die trying!”

Musk, a Twitter power user who currently has 93.7 million followers, has accused the company of displaying a left-wing bias and censoring conservative views. He’s said he wants to make Twitter strictly adhere to “free speech” principles in moderating content and users on its platform.