Elon Musk is seeking to end his $44bn (£36bn) bid to buy Twitter, alleging multiple breaches of the agreement.
The announcement is the latest twist in a long-running saga after the world's richest person decided to buy Twitter in April.
Mr Musk said he had backed out because Twitter failed to provide enough information on the number of spam and fake accounts.
Twitter says it plans to pursue legal action to enforce the agreement.
"The Twitter Board is committed to closing the transaction on the price and terms agreed upon with Mr. Musk," Twitter chairman Bret Taylor wrote in a tweet, setting up a potentially long and protracted legal battle between the two sides.