Slack, owned by Salesforce, is suing Microsoft in a UK lawsuit over its Teams bundling which it alleges is an anti-competitive practice.

Essentially, Slack alleges that Microsoft’s practices with its Teams app has harmed competition in the business messaging app arena, as it bundles Teams with other Microsoft products which Slack said “limit[s] customer choice.”

Microsoft says the complaint is unfounded, saying that Slack’s “lacklustre growth, compared to Zoom and Teams, was based on inferior capabilities when COVID-19 hit in 2020, and had nothing to do with ​Microsoft.”

The lawsuit follows on from a complaint from Slack to the European Commission back in 2020, saying that Microsoft’s bundling of Teams with other Office offerings gave the software an unfair advantage.

Microsoft then conceded to pressure from the EU, reducing prices on Office products that did not include Teams, avoiding a potential fine.

The firm moved to unbundle Teams globally in 2024, selling Teams separately from the rest of its standard Office offerings.

Recommended reading

• Google Urges CMA to Act Against Microsoft for Anti-competitiveness
• Microsoft Unbundles Teams from Office Suite, Globally
• EU Opens Microsoft Anti-Trust Probe Over Teams Bundling
• CMA Seeks Views on Microsoft Partnership With OpenAI

The tech giant is no stranger to anti-competition allegations, as the mass lawsuit has been approved for its next stage in the UK, alleging that Microsoft is overcharging businesses that use a rival cloud provider and its Windows software. Microsoft also denies the allegations brought up in this case.