Microsoft pledged last December to give European consumers better access to rival Internet browsers in Windows, ending a long antitrust dispute with the European Union.
In March and April, Microsoft is allowing Europeans to select among 12 browsers on almost 200 million old and new personal computers in Europe.
At first sight, Microsoft's browser Choice Screen (www.browserchoice.eu) shows its own Internet Explorer, Mozilla's Firefox, Apple Inc's Safari and Google Inc's Chrome. It is not immediately obvious that the remaining choices are available by scrolling to the right of the Web page.
Makers of those browsers -- Avant Browser, Flock, Green Browser, Maxthon, Slim Browser and Sleipnir -- urged the European Commission in a petition on Thursday to rectify the situation.
"We are only requesting the simple addition of any text or design element, that would indicate to an average user that there are choices 'to the right of the visible screen,'" the companies said in the petition.
Microsoft has said the screen was in compliance with the European Commission's decision.
Five largest browsers show directly on the Choice Screen, but smaller vendors say there are no real indication consumers could find more options right to the screen.
"The final Choice Screen design leaves the vast majority of users unaware that there are more than five browsers to choose from," smaller firms said in the petition.