Microsoft must face a major collective lawsuit in the UK over its cloud software licensing practices, after the Competition Appeal Tribunal allowed the case to move forward.
The claim, brought by Dr Maria Luisa Stasi, alleges that Microsoft abused its dominant position by making it more expensive to run its Windows Server software on rival cloud platforms than on its own Azure service. The case could cover around 59,000 organisations and seeks damages estimated at more than £1.7 billion.
At this stage, the Tribunal was not deciding whether Microsoft actually broke competition law. Instead, it assessed whether the case is suitable to proceed as a collective action. Microsoft had argued that the claim should be blocked, saying it lacked a clear plan for trial and relied on weak economic analysis. It also challenged the proposed opt-out structure, which would automatically include affected businesses unless they choose to leave the case.
The Tribunal rejected these arguments. It found that the claim has a realistic prospect of showing harm across the whole class. A key factor was the alignment between the claimant’s arguments and findings from the UK competition regulator, which previously concluded that Microsoft’s licensing practices can disadvantage rivals like Amazon and Google and reduce competition in cloud services.
The core allegation is not that competitors were fully pushed out of the market, but that Microsoft’s pricing and licensing rules made competition weaker. By increasing rivals’ costs, the claim argues, Microsoft may have steered customers toward Azure and softened price competition across the market.
The Tribunal accepted that this “market distortion” theory is relatively novel but still legally arguable. It also ruled that the case can proceed without relying on strict economic tests like a price-cost benchmark, which Microsoft had said were necessary.
Importantly, the Tribunal confirmed that the claim is suitable for collective proceedings on a class-wide basis. The alleged harm—higher prices paid by businesses using Windows Server in the cloud—can be assessed across the group, even if the detailed analysis will be complex.
The decision means the case will now move toward a full trial, where Microsoft will have the opportunity to defend its practices in detail.
