Twitter has hired US law firm Wachtell, Lipton, Rosen & Katz as it prepares to sue Elon Musk and force him to complete the $44 billion acquisition of the social media company, according to people familiar with the matter.

Musk, the chief executive officer of Tesla, on Friday terminated his deal, saying Twitter had failed to provide information about fake accounts on the platform, after which Twitter’s chairman, Bret Taylor, vowed a legal fight.

Twitter is planning to file a law suit early this week in Delaware, people familiar with the matter said.

Twitter declined to comment while the law firm did not immediately respond to Reuters’ request for comment outside business hours.

Wachtell, Lipton, Rosen & Katz was one of the legal advisers for Musk’s plan to take Tesla private in 2018. Musk tweeted that there was “funding secured” for a $72 billion deal to take Tesla private but did not move ahead with an offer.

Musk and Tesla each paid $20 million in civil fines, and Musk stepped down as Tesla’s chairman to resolve US Securities and Exchange Commission claims that he defrauded investors.

Twitter’s existing legal team includes Simpson Thacher & Bartlett LLP and Wilson Sonsini Goodrich & Rosati.