Musk says deal to buy Twitter can’t go forward unless the company can show that less than 5% of accounts are fake or spam.
The billionaire wrote a letter to Twitter on Monday.
Musk said the company was in a "clear material breach" of its obligations and that he reserves all rights to end the merger agreement.
In March, Musk had warned he would put the $44 billion deal “temporarily on hold” while he waited for data from Twitter.
In the letter submitted on Monday, Musk’s lawyers said that he believes the company “is actively resisting and thwarting his information rights.”
Twitter shares were down 5% early Monday.
Twitter has not commented on the letter.