Regulators are informally quizzing competitors and customers about how Microsoft may be abusing its access to business-sensitive information belonging to cloud firms it has commercial dealings with.
EU antitrust enforcers want to know whether Vole then users such confidential information to compete with cloud-service providers on the market.
The EU's escalation follows on the heels of a series of complaints from cloud firms over Microsoft's behavior -- including CISPE, an industry group with links to Amazon.com's Amazon Web Services.
The scrutiny of cloud competition coincides with Microsoft's efforts to convince regulators around the world to approve its $69 billion acquisition of Activision Blizzard, publisher of Call of Duty.
The European Commission, the EU watchdog, conditionally approved the tie-up, just weeks after the UK's competition authority vetoed it.