Slack CEO Stewart Butterfield as accused Microsoft of “surprisingly unsportsmanlike” behaviour while competing with the Microsoft Teams product, reports BusinessInsider.

While Slack welcomed Microsoft Teams with a full-page New York Times spread in 2016, Microsoft has been throwing its weight around, announcing in June this year that with 13 million daily active users it now had more active users than Slack.

Crucially Microsoft made its announcement during Slack’s pre-IPO quiet period, meaning they were not able to respond.

Recently Slack finally did, announcing that they had 12 million daily active users, but insisted its users were more engaged, and because Teams was bundled with Office, Microsoft’s numbers were “a little bit misleading in terms of what you’re measuring.”

Butterfield was now pulling no punches, saying the timing of Microsoft’s announcement was “kind of crazy” and that the Google Search term for Teams was how to uninstall it.

He suggested Microsoft saw Slack as an “existential threat”, saying “I think they’re in a zero-sum competition for prestige and power and compensation inside the organization.”

He said a lot of people were choosing Slack even when Teams were free and bundled and despite Microsoft engaging in “a very aggressive push to get people in there.”

Butterfield also implied Microsoft’s behaviour should attract anti-trust scrutiny.

“We see things like paying companies to use Teams and that leans on a lot of existing market power…maybe it’s something we should have a look at but we haven’t taken any action.”

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