Twitter is preparing for a legal battle with tech billionaire Elon Musk over his attempt to call off the takeover of the online service. The company did not violate the acquisition agreement – but Musk did.

In a letter to Musk’s legal representative, Twitter’s lawyers said his termination of the deal was “invalid and unlawful” from the company’s perspective. Contrary to Musk’s claims, Twitter did not violate the acquisition agreement, according to the letter published on Monday. Musk, on the other hand, knowingly and intentionally violated the agreement with his withdrawal.

Musk announced on Friday that he was withdrawing from the agreement to buy Twitter for around $44 billion. To justify this, he referred to his previously unsubstantiated claims that Twitter had significantly more fake accounts than the company’s estimate of less than five percent. His lawyers argued, among other things, that Twitter failed to fulfill its contractual obligation to provide Musk with the necessary data access to verify the numbers.

Twitter has already announced that it wants to go to court at the company’s official headquarters in the state of Delaware. There, the Delaware Chancery Court can also order the completion of a takeover.