Slack Sues Microsoft in UK Over Teams Bundling

Key Takeaways

• Slack filed the lawsuit on April 23 at London's High Court, alleging Microsoft's Teams bundling harmed competition
• Microsoft avoided EU fines last year by promising reduced prices for Office products excluding Teams
• A separate UK lawsuit alleges Microsoft overcharged British businesses for Windows Server on rival cloud services

The Lawsuit

Slack Technologies LLC and related companies filed a lawsuit against Microsoft at London's High Court on April 23. The complaint accuses Microsoft of anticompetitive practices related to its Teams collaboration app.

A Slack spokesperson said the lawsuit was filed "because Microsoft's practices harmed competition, using tying and bundling of Teams to limit customer choice." Microsoft did not immediately respond to a request for comment.

The core allegation: Microsoft bundled Teams with its Office productivity suite, making it harder for competing workplace messaging apps to win customers. When customers already get Teams included with their Office subscription, they have less incentive to pay for alternatives like Slack.

History With European Regulators

This lawsuit is not Slack's first antitrust action against Microsoft. In 2020, Slack complained to the European Commission about the same bundling practices. The company argued that Microsoft used its dominant position in office productivity software to gain an unfair advantage in the workplace messaging market.

Microsoft avoided a potentially hefty fine from the European Commission by promising reduced prices for Office products excluding Teams. That agreement came last year. But that deal covered EU markets. It did not resolve Slack's grievances in the UK, which is no longer part of the European Union.

Microsoft Faces Multiple UK Legal Challenges

The Slack lawsuit arrived in the same week that London's Competition Appeal Tribunal certified a separate mass lawsuit against Microsoft. That case alleges Microsoft overcharged British businesses to use Windows Server software on cloud computing services provided by rivals.

Microsoft disputes the allegations in the Windows Server case. The company now faces two parallel legal challenges in the UK, both centered on claims that it uses its market position to disadvantage competitors and their customers.

What Bundling Means for Business Buyers

The bundling question matters for any company buying workplace software. When Microsoft includes Teams at no extra cost with Office 365 or Microsoft 365 subscriptions, IT departments face a basic question: why pay separately for Slack?

Slack's argument is that this setup is not fair competition. Microsoft controls the productivity suite most large companies already use. By including Teams free, Microsoft can win the messaging market without Teams being the better product.

Microsoft's counter-argument, implied by its EU settlement, is that customers can now buy Office without Teams at a lower price. Customers who prefer Slack or other alternatives can save money and use their preferred tool.

What Happens Next

UK antitrust cases typically take years to resolve. The Competition Appeal Tribunal and High Court move slowly, and appeals are common. Microsoft may seek to settle the UK case as it did with the European Commission, or it may fight the allegations in court.

For now, Slack has established a new legal front in its long-running dispute with Microsoft. The outcome could affect how software giants structure their product bundles across Europe and beyond.

Frequently Asked Questions

Why is Slack suing Microsoft in the UK?

Slack alleges Microsoft bundled Teams with Office products to limit customer choice, harming competition in the workplace messaging market. The lawsuit was filed at London's High Court on April 23, 2025.

Did Microsoft already settle this issue with the EU?

Yes. Microsoft reached an agreement with the European Commission in 2024, offering reduced prices for Office products excluding Teams. However, that settlement applies to EU markets, not the UK.

What is product bundling in antitrust law?

Product bundling occurs when a company includes multiple products together, potentially making it harder for competitors to sell alternatives. Antitrust law examines whether bundling by dominant companies unfairly restricts competition.

How long will the UK lawsuit take?

UK antitrust cases typically take several years to resolve. Microsoft may seek to settle or contest the allegations through trial and potential appeals.

What other legal challenges does Microsoft face in the UK?

London's Competition Appeal Tribunal certified a mass lawsuit alleging Microsoft overcharged British businesses to use Windows Server on rival cloud services. Microsoft disputes those allegations.

Source: Tech-Economic Times / ET