Microsoft is testing pop-up warnings that trigger when users start to install the Chrome or Firefox web browsers.
The warnings appear on Windows 10 and remind people they already have Microsoft's Edge browser installed.
Text in the pop-up claims that Edge is a "faster, safer" browser for the Windows 10 operating system.
The prompts are included in versions of Windows 10 that trial novel future features.
In a statement, Microsoft said the warning windows were being tested with a small number of users who were part of its "Insiders" initiative.
"The Windows Insider Program enables Microsoft to test different features, functionality and garner feedback before rolling out broadly," said the statement.
The warnings did not stop any software being installed, said Microsoft.
"Customers remain in control and can choose the browser of their choice," it said. The warning panel links to a user settings system that lets them turn off the alerts.
In the past, Microsoft has been harshly penalised for using its dominance in desktop computing to push people towards its products. It has paid billions in fines for not doing enough to let people know about rival browsers.
The prompt is one of several features being tested prior to potential inclusion in the October update for Windows 10.
The BBC understands that, unlike some of the other new features in the prototype being tested by Insiders, the warnings will not be rolled out to the larger population of Windows 10 users in the next update.