A hot potato: Big tech companies including Facebook, Apple, Amazon and Google have been under a ton of antitrust scrutiny as of late, with Microsoft surprisingly being the one that had managed to stay under the radar. That may start to change, with Slack accusing the Redmond giant that it is boosting adoption for its competitor work chat app by forcing it onto Office 365 customers.

Slack has filed an antitrust complaint against Microsoft in the European Union, alleging the latter company is stifling competition with unfair practices such as bundling its collaboration app, Teams, with its Office productivity suite.

In the complaint, Slack alludes to the way Microsoft did things with Internet Explorer, a web browser that achieved incredible adoption numbers by virtue of being bundled with the Windows operating system. Slack believes that Teams is being forced onto Office 365 customers, who are seemingly unaware of the added cost and don't have the option to remove it.

Last May, Slack CEO Stewart Butterfield insisted that Microsoft Teams is not a competitor to Slack and that Microsoft baking it into its productivity suite was a move made in frustration over low adoption numbers. Now that teleconferencing apps have seen a surge in demand, that position has changed to acknowledge that Teams and Slack do have some similarities in terms of their overall scope.

In a statement today, Slack VP of Communications and Policy Jonathan Prince explained that "Slack threatens Microsoft’s hold on business email, the cornerstone of Office, which means Slack threatens Microsoft’s lock on enterprise software."

He also noted that Microsoft wants to dominate their customers' entire software stack, while Slack is designed as a piece of the puzzle that organizations can use as part of their custom mix of productivity tools.

The European Commission will now review the antitrust complaint to decide on whether an investigation is in order. But while Slack is asking the EU to level the playing field, the complaint comes at a time when the two companies are fighting to dominate the future of workplace collaboration. To see that, look no further than Slack's recent partnerships with IBM and Amazon, its largest customers to date.