Elon Musk has threatened to walk away from his $44bn takeover of Twitter.
He is accusing the social media company of “thwarting” his requests to learn more about its user base.
According to a report by BBC, Mr. Musk said he was entitled to do his own measurement of spam accounts.
The letter formalizes a dispute that has simmered for weeks after Mr. Musk declared the deal “on hold” pending further information.
Mr. Musk has said he believes spam and fake accounts represent a far greater share than the less than 5% of daily users that Twitter reports publicly.
Twitter, which has said Mr Musk waived typical rights to due diligence in his eagerness to clinch the deal, added that it intended to complete the takeover at the agreed price and terms.
Mr Musk, who faces a $1bn break-up fee and possible lawsuit if he opts out, first raised the issue of the spam accounts on social media last month, saying the deal was on hold but he remained committed to the acquisition.
Analysts have said the Tesla boss might be using the issue to try to renegotiate the price or even walk away.
