Dr. Maria Luisa Stasi has filed a Collective Proceedings Order (CPO) application to consolidate thousands of UK businesses into an opt-out collective action. The claim alleges that Microsoft charged higher fees for running Windows Server on competing cloud platforms such as AWS, Google Cloud, and Alibaba than it did for Microsoft Azure.
The CAT has scheduled a one-day hearing, with a reserve day, on 11 December 2025, to determine whether the claim should be certified as a CPO. The class representative’s filings and public outreach estimate potential damages at around £2 billion, and the CAT previously gave Microsoft until 25 July 2025, to file its initial response, followed by the claimant’s reply by 10 October 2025.
The litigation runs alongside active regulatory scrutiny of the cloud industry. On 28 January 2025, the UK Competition and Markets Authority (CMA) released provisional findings from its market investigation into cloud services, indicating that competition in the UK cloud sector is not functioning optimally. The CMA also highlighted concerns that licensing practices, including those of Microsoft, could potentially harm competition.
Similarly, the European Commission has initiated coordinated inquiries into cloud market behavior under the Digital Markets Act, reflecting broad regulatory interest in cloud licensing and portability. These concurrent regulatory actions significantly enhance the evidence base and political landscape supporting the claim.
Microsoft reportedly increased the costs and, at times, the legal hurdles for customers running Windows Server workloads on AWS, Google Cloud, and Alibaba, compared to Azure. The complaint argues this strategy effectively nudges—or forces—customers toward Azure, thereby diminishing competition in the IaaS and PaaS markets and raising prices for end users.
The proposed class includes UK-domiciled organizations that paid to run Windows Server on the listed competing clouds, with the claim specified to cover usage since December 2018. The applicant estimates collective damages at around £2 billion.
