The European Commission this week announced that it will be keeping a close eye on Microsoft's Windows RT operating system, in response to Mozilla's complaint that the forthcoming platform excludes third-party browsers. At issue is a 2009 antitrust decision that requires Microsoft to provide links to other browsers from within a Windows ballot display. According to Mozilla, though, only Internet Explorer can run in the Classic environment on RT, suggesting that Microsoft's ARM variant of Windows 8 may violate European regulations.

In an e-mail to reporters, EC spokesman for competition Antoine Colombani confirmed that "the Commission is aware" of Mozilla's claims, and that it "will remain vigilant" in overseeing Microsoft's compliance with current regulations. Colombani stressed, however, that the EC's 2009 decision applies only to PCs. This stipulation is of particular significance since Windows RT would primarily run on tablets, though it could run on ARM-based PCs, as well. This has led some to speculate that Microsoft may be taking advantage of a perceived loophole in current regulations, but the company has thus far declined to comment on the matter.

Regulators in the US, meanwhile, are taking a similarly exploratory approach to Windows RT. On Tuesday, a spokesperson for Sen. Herb Kohl told TechWorldNews that the Senate Judiciary Committee plans to look into allegations that the operating system infringes browser competition, as part of a fact-finding "preliminary inquiry." Antitrust, as in Europe, is at the center of Microsoft's stateside controversy, though it's worth noting that relevant US regulations apply specifically to "Intel-compatible PC operating systems," whereas those in Europe mention only PCs in the abstract.

The European Commission's ruling is set to expire in 2014, and if Microsoft is found to be in violation, it could be fined up to ten percent of its annual revenue.