Elon Musk's decision to back out of his $44 billion purchase of Twitter.
Both parties are preparing for what is expected to be an acrimonious and protracted judicial battle.
Musk made the announcement in a filing to the Securities and Exchange Commission on Friday.
Twitter has been accused of withholding important information on the frequency of spam and false accounts on its platform.
The CEO of Tesla claims that Twitter violated the Texas Securities Act, breached a contract, and committed fraud.
Musk's counterclaims were submitted under seal to the Delaware Chancery Court last week.
Earlier this year, Musk made an offer to purchase the company.
Then attempted to back out of the agreement by alleging that the social media platform was considerably more heavily populated with "spam bots" and phoney accounts than Twitter had admitted
Twitter filed a lawsuit to compel him to finish the deal. Musk's countersuit was filed in response.