EU antitrust authorities will open an investigation next week into whether Microsoft (NASDAQ:MSFT) is unfairly bundling its Teams video conferencing app with its Office service, according to a Financial Times report on Monday.

Sources quoted by the paper say the probe could lead to formal charges as soon as the early autumn. Regulators at the European Commission, the executive body of the EU, are worried that previous attempts by Microsoft to assuage competition concerns have been insufficient, the sources added.

In July 2020, messaging app Slack filed a complaint with the EU Commission, arguing that “Microsoft […] illegally tied its Teams product into its market-dominant Office productivity.” Brussels has said that there are other complainants besides Slack, which is now owned by Salesforce (NYSE:CRM).

Microsoft reportedly agreed to quit forcing Office customers to install Teams automatically earlier this year in response, the FT said.

However, the paper noted that recent talks between Microsoft and EU officials came to a halt over the wider geographical impact of the tech giant’s concessions and the amount the company would charge for Teams.

The chance that Microsoft avoids an investigation by the EU is now “very unlikely,” people with knowledge of the matter told the FT. It would be the first probe carried out by EU officials into Microsoft since 2008 when the firm was accused of tying together its Internet Explorer browser and its Windows operating system.