Slack said the issue was Microsoft's Teams productivity software, which was introduced in early 2017 to compete with Slack's chat app and others in the fast-growing and lucrative workplace collaboration market.

Slack said on Wednesday that it has filed a complaint against Microsoft with the European Commission.

"What we asking for is Teams be separated from the Office Suite and sold separately with a fair commercial price tag, so it competes on the merits with our products," its general counsel David Schellhase told reporters.

The company accused Microsoft of illegally tying its Teams product into its market-dominant Office productivity suite, force installing it for millions, blocking its removal, and hiding the true cost to enterprise customers.

Microsoft said it look forward to providing information to EU competition enforcers.

"We created Teams to combine the ability to collaborate with the ability to connect via video, because that's what people want. With COVID19, the market has embraced Teams in record numbers while Slack suffered from its absence of video-conferencing," a Microsoft spokeswoman said.

"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."

Videoconference has seen a surge in demand as employees work remotely due to lockdowns aimed at slowing the spread of the coronavirus. Other players include Zoom Video Communications, Alphabet's Google, Facebook and Cisco.

Schellhase said it was possible Slack could take its grievance to U.S. antitrust enforcers in future.

"We have not taken similar actions in the U.S. but we are having conversations with relevant U.S. authorities as well," he said.

The Commission, which has fined Microsoft a total 2.2 billion euros ($2.6 billion) in a decade-long investigation involving tying cases and other practices, confirmed receipt of the complaint, saying that it would assess it under its standard procedures.

By Foo Yun Chee