Salesforce and Slack have escalated their long-running dispute with Microsoft by filing a lawsuit in London’s High Court to accuse the tech giant of anticompetitive behavior tied to its Teams product, per Reuters.
The claim, lodged on April 23, centers on Microsoft’s practice of bundling Teams with its Office suite – a strategy that Slack argues limits customer choice and restricts fair competition in the workplace collaboration market.
A Legal Battle in an Uneven Market
This lawsuit doesn’t come out of the blue. Slack has long argued that Microsoft’s ability to package Teams within widely used enterprise software gives it a structural advantage that competitors struggle to match. Slack first raised this issue with European regulators all the way back in 2020.
Regulatory pressure has already forced some changes, with Microsoft previously adjusting its pricing in Europe and ultimately offering Office packages without Teams at a lower cost to address competition concerns.
However, this new UK lawsuit suggests that Slack and its parent company, Salesforce, believe those changes have not gone far enough.
The legal action also comes at a time of heightened scrutiny for Microsoft in the UK. In the same week, a separate case was approved alleging that the company overcharges businesses for running Windows Server on rival cloud platforms.
SF Ben reached out to Microsoft for comment, to which they responded: “Salesforce’s complaint lacks merit and we’ll make our case before the Court in due course. Slack’s lackluster growth, compared to Zoom and Teams, was based on inferior capabilities when COVID 19 hit in 2020, and had nothing to do with Microsoft.”
Beyond the legal arguments, there’s no question about Microsoft Teams’ current advantage in the workspace collaboration market. Teams has reached around 320 million monthly active users and holds approximately 37% of the collaboration software market as of November 2025, according to SQ Magazine.
Slack, by comparison, sits closer to 13% market share, with 79 million active users (as of November 2025) and slower growth in recent years.
This is attributed by some to Microsoft’s distribution. By embedding Teams into Microsoft 365, the company has been able to scale rapidly across the enterprise – particularly with large and regulated companies.
Slack, meanwhile, has taken a different path. Backed by Salesforce since its $27.7B acquisition in 2021, it continues to position itself as more of a flexible, integration-friendly platform, well adopted among smaller, agile teams.
Notably, SQ Magazine’s research suggests that Slack users report higher levels of empowerment when making strategic decisions than Teams users.
A spokesperson from Slack told SF Ben: “We are dedicated to fostering a competitive marketplace that promotes innovation and ensures the broader tech ecosystem remains open to all. We filed our legal claim because Microsoft’s practices harmed competition, using tying and bundling of Teams to limit customer choice.
“Our priority remains centered on customer choice and interoperability, advocating for a free and fair digital landscape.”
Final Thoughts
This lawsuit seems like a continuation of a long-running tension between two fundamentally different approaches to enterprise software.
Whether Microsoft’s approach crosses the line into anticompetitive behavior will ultimately be decided in court. But there feels like there’s a bigger question here. In a market where “automation, AI, and ecosystem integration” are key drivers of growth, would any vendor act differently given the same opportunity?
Make sure to leave your thoughts in the comments below.
