Microsoft's turn was sued by the European Union (EU) because their Teams teleconferencing software offering was found to be in violation of the anti-monopoly act. Offering Teams along with Microsoft 365 and Office 365 subscription bundles is said to be Microsoft's attempt to monopolize the Software as a Service (SaaS) market for professional use.
Although Microsoft no longer offers Teams together with Microsoft 365 and Office 365 since last April, the EU feels that this action is still insufficient because the integration of Teams is still offered through their other software. This in the EU's view gives Teams an unfair advantage making it difficult for competitors to offer their software to Microsoft customers.
This is not the first time Microsoft has faced accusations of monopolizing the market. Previously they were fined by the EU for offering Internet Explorer and Windows Media Player which was also said to make it difficult for competitors to offer products with similar functionality.