Microsoft could face a new EU anti-trust challenge over the bundling of accounting software with an upcoming version of its Office productivity suite.

Accounting software specialist Sage has said it plans to raise its concerns about the bundling with the European Commission, if the Commission does not address it on its own.

A company spokesman said that Sage would be "very surprised" if the Commission did not investigate the inclusion of Microsoft Office Small Business Accounting financial management software with an edition of Office due out late this year. The edition is designed for businesses with up to 25 employees, and offers management of sales orders and other business data.

But Sage has stopped short of saying it will file a formal complaint. The regulatory body is aware of the issue but has not received any complaints regarding the business accounting software market, a spokesman for the Commission said.

The potential challenge comes as Microsoft is still appealing anti-trust rulings made by the Commission last year. The Commission ruled in March that the software maker had abused its dominance in the desktop operating system market to gain an edge in related markets, specifically media players. It ordered the company to pay a 497 million euro fine and offer a version of Windows without its media player. The Commission also ordered Microsoft to publish APIs for its server software that would make it easier for competitors to make products that work well with Windows.

The inclusion of the accounting software could be seen as an another effort by the software giant to leverage its desktop dominance to cut out rivals, according to Sage.

Microsoft has pointed out that Office for Small Business Management is just one version of Office that will be available. The small business edition is also built using open interfaces, Microsoft has said.

Sage will wait until the Office edition is released in the US to see how it's packaged and priced, said its spokesman. "If it offers the same level of integration for third-party vendors, that would be pretty fair," he said.