Thousands of British companies are being urged to come forward after a £2bn class action lawsuit was launched against Microsoft, alleging the tech giant overcharged customers who used its Windows Server software on rival cloud platforms such as Amazon Web Services (AWS), Google Cloud and Alibaba Cloud calculated.
The case, filed with the UK Competition Appeal Tribunal (CAT), was led by Dr. Maria Luisa Stasi, a leading expert in the regulation of digital markets. She is seeking damages for companies that are forced to pay excessive prices due to Microsoft’s restrictive licensing practices.
“If your company has used Windows Server on Google, Amazon or Alibaba’s cloud platforms at any time since December 2018, you have probably paid too much money,” said Dr. Stasi. “This lawsuit is intended to put an end to that.”
“Those responsible for IT or cloud contracts should get in touch. Billions have been taken away from corporate budgets due to Microsoft’s licensing practices.”
The lawsuit from Dr. Stasi could become one of the largest antitrust lawsuits ever filed in the UK tech sector, potentially affecting tens of thousands of organizations from start-ups to multinational corporations.
The lawsuit closely follows the Competition and Markets Authority’s (CMA) final report on the UK cloud computing market, which concluded that Microsoft’s software licensing practices were “adversely affecting competition”.
The CMA found that Microsoft’s pricing model makes it more expensive for customers to run its software on competing clouds than on its own Azure service, effectively penalizing companies for using competitors’ infrastructure.
These findings are directly consistent with the case of Dr. Stasi will be heard again in court on December 11, 2025 to decide whether he can proceed to a full trial.
Legal experts say the case could set a precedent for class action lawsuits against dominant technology companies accused of abusing market power in software and cloud services.
Cloud costs are rising for UK businesses
The legal action comes amid increasing pressure on companies struggling with rising cloud costs.
Recent research shows that 67% of UK IT leaders expect their cloud spending to increase further next year, with 68% of companies already making cuts in other IT areas to compensate.
Smaller organizations are particularly affected. Many lack the resources to navigate complex licensing models or negotiate tailored cloud contracts, leaving them vulnerable to hidden cost differences.
“Cloud costs for UK businesses are rising rapidly,” said Dr. Stasi. “Contacting you doesn’t commit you to anything, but it could result in your company reclaiming a significant portion of its IT budget.”
The case against Microsoft is part of a broader wave of investigations targeting Big Tech’s control of the global cloud market.
Regulators across Europe, the United States and Asia have stepped up investigations into whether big technology companies are using software dominance to tighten control over infrastructure markets.
In May 2025, the European Commission also expressed concern about “loyalty-enhancing pricing” in cloud software licensing, echoing the CMA’s conclusions.
Microsoft has repeatedly defended its practices, saying its licensing models are “pro-competitive” and designed to “provide customers with choice and flexibility.”
If the CAT rejects Dr. Stasi certifies as a class action lawsuit, affected organizations could be automatically included if they do not withdraw.
What happens next?
A procedural hearing is scheduled for December 2025, after which the court will decide whether to send the case for trial. If successful, the remuneration could be distributed across all qualifying UK companies that used Windows Server in competing clouds after December 2018.
Legal analysts say the potential £2 billion claim underlines the increasing use of competition-style class actions in the UK post-Brexit, allowing domestic courts to deal with global technology disputes previously handled in Brussels.
For now, companies are recommended to register interest or provide usage data – a process that does not impose a requirement to join but may determine eligibility for compensation later.
