Microsoft gives its Edge web browser an unfair advantage and EU antitrust regulators should subject it to tough EU tech rules, three rival browsers and a group of web developers said in a letter to the European Commission.

The move by Vivaldi, Waterfox, Wavebox and the Open Web Advocacy could boost Norwegian browser company Opera which in July took the European Commission to court for exempting Edge from the Digital Markets Act (DMA).

The landmark DMA set out a list of dos and don'ts for online services deemed as gateways for businesses to reach end-users, with the aim of making it easier for consumers to pick and choose services from different providers.

The companies and the advocacy group said they supported Opera's challenge.

"It is paramount that the Commission reconsiders its position," they said in a letter dated Sept. 17 seen by Reuters.

"Unfair practices are currently allowed to persist on the Windows' ecosystem with respect to Edge, unmitigated by the choice screens that exist on mobile," they said, pointing to Edge set as the default browser on all Windows computers.

"No platform independent browser can aspire to match Edge's unparalleled distribution advantage on Windows. Edge is, moreover, the most important gateway for consumers to download an independent browser on Windows PCs."

The Commission and Microsoft declined to comment. Edge's global market share is just over 5% while market leader Google's Chrome is 66% according to StatCounter.

Vivaldi, Waterfox, Wavebox and Open Web Advocacy also alleged that pop-up messages on Edge mischaracterize the features of rival browsers that differentiate them from the Microsoft product.

The European Commission in its February decision said it did not consider Edge a gatekeeper and that the DMA requires Microsoft to allow users to easily uninstall any software apps.