Business communications platform Slack Technologies announced Wednesday that it had filed an antitrust complaint against Microsoft Corp. in the European Union (EU).

In the complaint, Slack accuses Microsoft of trying to eradicate competition through tying its Microsoft Teams product to Microsoft Office. Slack alleges that Microsoft has engaged in illegal and anti-competitive practices, “abusing its market dominance to extinguish competition in breach of European Union competition law.”

The complaint alleges that Microsoft illegally connected its Microsoft Teams product to Office, which it then force installed for millions, blocking its removal, and hiding the true cost to enterprise customers. Microsoft Teams, like Slack, is a communication and collaboration platform. Slack likened this action to Microsoft’s past decision to tie Internet Explorer to Windows, which was subject to a lawsuit, United States v. Microsoft, in 1999.

This complaint adds another big name to the major US and EU tech companies currently under investigation for allegedly abusing their market dominance. In March 2019, Spotify filed an antitrust complaint against Apple in the EU. European Commission Competition Commissioner Margrethe Vestager has brought fines against Google and is investigating other major US tech companies, including Amazon, Apple, and Facebook. 

The European Commission will now review the complaint and determine whether to formally investigate Microsoft’s allegedly illegal practices.