Slack has filed a competition complaint against Microsoft with the European Commission, saying it is “force-installing” Teams and blocking its removal.

“We’re asking the EU to be a neutral referee, examine the facts, and enforce the law,” said David Schellhase, General Counsel at Slack in a statement today.

The California-based company wants the Commission to force Microsoft to sell Teams as a separate product, saying it is “abusing its market dominance to extinguish competition in breach of European Union competition law.”

(Slack, an enterprise collaboration platform provider, went public in 2019, citing a potential $28 billion market opportunity. It started trading at $38.50/share but has seen its shares fall, despite the wholesale shift to remote working globally.)

“Microsoft is reverting to past behavior”, Schellhase said.

“They created a weak, copycat product and tied it to their dominant Office product, force installing it and blocking its removal, a carbon copy of their illegal behavior during the ‘browser wars’. Slack is asking the European Commission to take swift action to ensure Microsoft cannot continue to illegally leverage its power from one market to another by bundling or tying products.”

Four years ago Slack paid for a full-page newspaper ad to “welcome” Microsoft Teams as a competitor, but as since been overtaken in terms of daily active users. Microsoft said it had 75 million Teams users in April.

Slack meanwhile cited 12 million daily active users in October 2019 and said it had added 90,000 net new users in Q1. The company in June also announced that it was migrating all of its native voice and video calling capabilities on to Amazon’s Chime — as Amazon also become Slack’s largest customer in Q1.

Microsoft said in an emailed comment: “We created Teams to combine the ability to collaborate with the ability to connect via video, because that’s what people want.  With COVID-19, the market has embraced Teams in record numbers while Slack suffered from its absence of video-conferencing.

“We’re committed to offering customers not only the best of new innovation, but a wide variety of choice in how they purchase and use the product.

“We look forward to providing additional information to the European Commission and answering any questions they may have.”