Twitter sent a letter to Microsoft CEO Satya Nadella accusing Microsoft of violating the social network's rules for developers who access the platform's data.
The letter, which was signed by Musk attorney Alex Spiro, states that Microsoft may have been in violation of multiple provisions of the agreement for an extended period of time.
In April, Microsoft stopped accessing Twitter data after opting not to pay fees that Musk demanded developers pay for APIs (application programming interfaces) that engage with the platform.