The Competition Appeal Tribunal (CAT) has ruled to certify a £2bn legal opt-out collective action against Microsoft over its cloud computing and software practices.
The court case, brought by digital markets regulation expert Dr Maria Luisa Stasi, accuses Microsoft of overcharging UK businesses and organisations that use its Windows Server on rival cloud services.
In its ruling, the CAT dismissed Microsoft’s arguments against certification and granted a Collective Proceedings Order (CPO) on an opt-out basis, allowing the case to head to trial. The CPO allows businesses to pursue legal action against Microsoft as a group as opposed to filing individual claims.
The CAT concluded in the ruling that the claim “comfortably crosses the hurdle of having a real prospect of success.”
The ruling to progress the claim to trial means UK businesses that have used Windows Server on rival cloud services can visit the claim’s website to find out about compensation. The case seeks compensation for approximately 59,000 businesses and organisations.
“Today’s ruling is an important moment for the thousands of organisations impacted by Microsoft’s conduct and in ensuring that a critical sector of the economy is innovative and open,” says Stasi.
“For years, Microsoft’s practices have had real financial impact on both public and private organisations. I’m now looking forward to preparing for trial and getting their money back on their behalf.”
Microsoft’s dominance and practices in its cloud and server operating systems have been subject to increasing scrutiny from regulators both in the UK and around the world.
In March, the UK Competition and Markets Authority announced it would launch an investigation into Microsoft, probing its software licensing practices in the cloud market. This investigation builds on a previous investigation concluded in July 2025 concerning Microsoft’s anti-competitive behaviour in cloud computing.
