US tech giant Microsoft is facing an antitrust complaint filed by three European rivals in the booming cloud computing business, one of the plaintiffs said on Thursday. The complaint, filed with the European Union's competition watchdog months ago, alleges that Microsoft's contractual and business practices make it costly and difficult for users of its cloud computing services to opt for those of a competitor, a source close to the matter said.

French cloud computing services provider OVHcloud confirmed in a statement that it had joined the complaint against Microsoft. A spokesperson for the company declined to give the names of the two other European plaintiffs.

"Through abusing its dominant position, Microsoft undermines fair competition and limits consumer choice in the cloud computing services market," OVHcloud said.

The Wall Street Journal was first to report the news.

The European Commission confirmed that it had received a complaint, without elaborating.

"We're continuously evaluating how we can best support partners and make Microsoft software available to customers across all environments, including those of other cloud providers," a spokesperson for Microsoft said in response to an e-mail seeking comment.

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