A Spanish association representing open-source software users has filed a complaint against Microsoft Corp to the European Commission, in a new challenge to the Windows developer following a hefty fine earlier this month.

The 8,000 member-strong Hispalinux, which represents users of the Linux operating system, said Microsoft had made it difficult for users of computers sold with its Windows 8 platform to switch to Linux and other operating systems.

Lawyer and Hispalinux head Jose Maria Lancho said he delivered the complaint to the Madrid office of the European Commission at 0900 GMT on Tuesday.

In its 14-page complaint, Hispalinux said Windows 8 contains an "obstruction mechanism" called UEFI Secure Boot that controls the start-up of the computer and means users must seek keys from Microsoft to boot up another operating system.

The group said it was "a de facto technological jail for computer booting systems ... making Microsoft's Windows platform less neutral than ever."

"This is absolutely anti-competitive," Lancho told Reuters. "It's really bad for the user and for the European software industry."

The European Commission fined Microsoft, global leader in PC operating systems, 561 million euros ($729 million) on March 6 for failing to offer users a choice of web browser. – Reuters