Elon Musk has threatened to sue Microsoft for allegedly using Twitter data without permission.
The billionaire's warning, via a tweet, came after the tech giant revealed it would drop his social media site from its corporate advertising platform.
Microsoft's service uses AI to help ad buyers manage their social media accounts in one place.
Musk said the firm had trained it "illegally using Twitter data", adding: "Lawsuit time."
Microsoft has indicated that its service will still support Meta's Facebook and Instagram.The company declined to comment when contacted by Sky News.
Microsoft's move comes after Twitter started charging companies for the data it collects from its users, which is essential for targeted advertising.
For a minimum of $100 a month, Musk's platform says it helps businesses "understand, track, and benchmark the conversations and perceptions surrounding your brand".
The service is known as an API (or application programming interface), and Twitter previously provided free access.
But just as Musk has sought to boost Twitter's finances by monetising users with a monthly subscription, which grants members with a blue verified checkmark, so too has he looked to bring in more cash from companies.
Mike Rhodes, CEO and founder of marketing agency ConsultMyApp, said: "Twitter has a vast amount of data, and it appears Musk is trying to leverage this, in part at least, to improve his advertising offerings.
"The social platform's advertising revenue has fallen off a cliff since he took over."
Musk made several dire assessments of Twitter's finances shortly after his $44bn (£38bn) takeover last October, claiming the company may face bankruptcy.
He later said the company's finances had stabilised, helped by thousands of lay-offs.
Musk's threat comes after he announced plans for his own chatbot to rival the Microsoft-backed ChatGPT, which he claimed has been trained "to be politically correct".
The SpaceX and Tesla owner was a co-founder of ChatGPT creator OpenAI, but left in 2019 and its biggest financial supporter is now Microsoft.
The Windows and Xbox maker has invested billions into the company, and rolled its GPT model into products like its Bing search engine and Office apps.