Slack, the company behind the popular messaging platform of the same name, on Wednesday filed a competition complaint before the European Commission against its main rival, Microsoft.

The San Francisco-based company alleges that Microsoft abused its market dominance by bundling two of its products, making it impossible for millions of customers to use its popular "office productivity suite" – which includes Word, PowerPoint, Excel and Outlook – without also installing its "Microsoft Teams" collaboration software. Microsoft Teams is similar to Slack's widely used channel-based messaging platform.

Slack has turned to Quinn Emanuel Urquhart & Sullivan's antitrust team to advise it through the process, according to people close to the matter.

According to a statement by Slack, Microsoft is trying to use its dominance in one market to gain a foothold in another market – a practice the company described as illegal and anti-competitive.

"We're confident that we win on the merits of our product, but we can't ignore illegal behavior that deprives customers of access to the tools and solutions they want," Jonathan Prince, vice-president of communications and policy at Slack, said in a statement published on the company's website.

"Competition and antitrust laws are designed to ensure that dominant companies are not allowed to foreclose competition illegally. We're asking the EU to be a neutral referee, examine the facts, and enforce the law," he added.

The European Commission will review Slack's complaint – which will not be made public under the Commission's rules – and decide whether to open an investigation in the coming months. There is no legal deadline to investigate competition complaints. Their duration depends on a number of factors, including the complexity of the case and the extent to which the companies concerned co-operate with the Commission.

Slack's prod to European officials to scrutinize the practices of its rival comes just as the bloc's executive arm has itself suffered major losses in disputes with two U.S. tech giants.

Last week, the European Court of Justice quashed a state aid decision by the Commission ordering the U.S. tech giant Apple to pay back €13.1 billion in unpaid taxes. One day later, the Luxembourg-based court also ruled that the U.S.-EU data protection agreement known as "Privacy Shield" did not meet GPDR standards, essentially ordering the Commission to work out a new deal with U.S. authorities.

Microsoft, based in Redmond, Washington, responded in a statement that its service differs from that offered by Slack.

"We created Teams to combine the ability to collaborate with the ability to connect via video, because that's what people want. With COVID-19, the market has embraced Teams in record numbers while Slack suffered from its absence of video-conferencing," the company said.