In a letter to the company, filed Friday with the Securities and Exchange Commission, Musk accuses Twitter of making "false and misleading representations" about the prevalence of fake accounts on its platform.
He says the company has not complied with its obligations to share data and information that he says he needs to evaluate its business.
"Sometimes Twitter has ignored Mr. Musk's requests, sometimes it has rejected them for reasons that appear to be unjustified, and sometimes it has claimed to comply while giving Mr. Musk incomplete or unusable information," Musk's lawyer, Mike Ringler, wrote.
Legal experts say this may not be sufficient grounds to break off the $44 billion deal without Musk being on the hook for a hefty fine. In response to Musk's letter, the chair of Twitter's board said it planned to sue.
"The Twitter Board is committed to closing the transaction on the price and terms agreed upon with Mr. Musk and plans to pursue legal action to enforce the merger agreement. We are confident we will prevail in the Delaware Court of Chancery," said Bret Taylor in a tweet, referring to a Delaware court that handles corporate disputes.
The billionaire CEO of Tesla and Space X struck a deal to buy the social media company back in April. But almost immediately, he started hinting – and then saying outright – that he had cold feet.
In May he declared the purchase was "on hold" while he looked into Twitter's accounting of how many users are not real people, but automated bots or spam. Soon after, Twitter agreed to give him access to its "firehose" – a real-time stream of more than 500 million tweets posted every day. Since then, the two sides have been sharing information and working to close the transaction.
On Thursday, the Washington Post reported the deal was "in jeopardy" because Musk doubts that Twitter's spam figures are verifiable. His team was "expected to take potentially drastic action," the Post reported.
Bots may not be the only factor in Musk's change of heart. While his offer of $54.20 a share was initially seen as a lowball price for Twitter, given that it was trading above $70 last year, tech stocks and the market as a whole have fallen sharply since he struck the deal.
Twitter shares are now trading around $37, down nearly 30% from the day Musk's purchase was announced. In May, Musk even said he might seek to negotiate a lower price.
On Thursday, Twitter had pointed to a statement the company issued in June saying it "has and will continue to cooperatively share information" with Musk and that "we intend to close the transaction and enforce the merger agreement at the agreed price and terms." The company was expecting to hold a shareholder vote on the deal by mid-August