A British watchdog agency said Tuesday it had complained to European Union regulators that Microsoft Corp.'s new file format for storing documents discouraged competition.

Britain's agency for education and information technology said it wanted to help the EU with an investigation it launched in January into whether the software giant deliberately withheld information from rivals. The current controversy centers on the ability of other companies to create products compatible with Microsoft's new file format, Office Open XML, which stores Word, Excel and PowerPoint files.

This comes on the heels of other EU antitrust action against Microsoft Corp. that resulted in $2.63 billion in fines over how Microsoft's Windows operating system works with rivals' programs and how it was bundled for sale.

The British Educational Communications and Technology Agency said it told the European Commission that barriers to interoperability - to programs working smoothly with one another - hurt students and teachers.

"Impediments to interoperability limit choice," the agency said. "In the context of the education system, this can result in higher prices and a range of other unsatisfactory effects."

Microsoft spokeswoman Anne-Sophie de Brancion said in an e-mail statement that the company would cooperate with the British agency and the European Commission.

"Microsoft is deeply committed to education and interoperability," de Brancion's statement said. She said the company has funded development of tools that help Microsoft "Office" programs work with files in what's known as OpenDocument Format.

The Redmond, Washington-based company is the largest software company in the world and one of the largest software suppliers to British schools.

In October, the British agency filed a complaint with Britain's Office of Fair Trading objecting to "the existence of impediments to effective interoperability in relation to Microsoft's 2007 product."

Critics of Microsoft's new Office Open XML, or OOXML, file format claim it locks out competitors, giving Microsoft customers no choice but to keep buying Microsoft programs forever. Microsoft claims its format is a more useful and varied alternative to OpenDocument Format, or ODF, which is backed by Sun Microsystems, IBM and others.

Office Open XML was last month approved as an international standard, which paves the way for it to be picked up by the IT departments of governments and large corporations.

The British agency said problems using Office 2007 software would be compounded by Microsoft's refusal to offer the same support to users of OpenDocument Format that it gives to Office Open XML.

"Such circumstances would constitute a barrier to the uptake and use of competitor products and limit competition and choice for educational users," the agency said.

The agency also said British regulators were still looking into its complaint about Microsoft's license conditions for school software, where the agency alleged "anticompetitive licensing practices."

In 2005, the British watchdog agency said primary schools could save up to 50 percent and secondary schools up to 25 percent if they dumped proprietary software - like Microsoft's - in favor of free, or open source, products.