Twitter is accusing Microsoft of abusing its data access privileges to its platform, in the latest sign of the social network’s owner Elon Musk igniting a feud between the two tech companies. In a three-page letter to Microsoft CEO Satya Nadella — and sent by Alex Spiro, Musk’s outside lawyer — Twitter accuses Microsoft of over-using its ability to download tweets from the platform, in an alleged violation of the social media company’s terms. Microsoft products, including Xbox One, Bing, Azure, Power Platform and Microsoft Ads, have “retrieved over 26 billion tweets in 2022 alone,” according to the letter, a level of usage it said could be considered “excessive or abusive.” “Our recent review of Microsoft’s activity on the Microsoft Apps indicates that Microsoft may have been in violation of multiple provisions of the Agreement for an extended period of time,” said the letter, a copy of which was reviewed by CNN, and referring to Twitter’s developer agreement. The letter also listed a number of other alleged violations, including an apparent failure to state a purpose for some of Microsoft’s data collection and, in other cases, use of the data in connection with “automation capabilities” subject to Twitter restrictions. The letter comes as Twitter is racing to find ways to boost revenue and cut costs after Musk took on a significant amount of debt to help finance his $44 billion acquisition of the company. Microsoft refused to pay Twitter to maintain its data access through Twitter’s application programming interface (API) after Twitter erected a paywall seeking to charge for data, according to the letter. The letter called on Microsoft to provide information about its past two years of Twitter API usage, setting a deadline of June 7. “We heard from a law firm representing Twitter with some questions about our previous use of the free Twitter API. We will review these questions and respond appropriately,” a spokesperson for Microsoft said in a statement. “We look forward to continuing our long term partnership with the company.” In recent months, Musk has stepped up his criticism of Microsoft as a perceived rival in artificial intelligence development, a field that relies heavily on ingesting publicly available online content such as tweets. After Twitter announced plans this year to charge for API access — which organizations later learned could cost them as much as $210,000 a month — Microsoft’s advertising platform said it would no longer support integration with Twitter. Musk reacted with a tweet saying Microsoft had “illegally” used Twitter data to train its AI and warned it was “lawsuit time.” He also accused Microsoft of “ripping off the Twitter database, demonetizing it (removing ads) and then selling our data to others.” In another tweet earlier this year, Musk blasted OpenAI, the maker of ChatGPT, for being “effectively controlled by Microsoft.” Microsoft has invested billions in ChatGPT’s creator OpenAI and integrated ChatGPT into its Bing search engine. But Nadella said this week in an interview with CNBC that Musk’s claim about control is “factually not correct.” “We have a noncontrolling interest in it, we have a great commercial partnership in it,” Nadella said of OpenAI. Musk’s targeting of Microsoft over its AI investments appears closely linked to his overall criticisms of existing AI models. Musk has vowed to develop a rival AI he calls “TruthGPT” to counter what he has described as excessive political correctness in mainstream models.